This reverts commit 02b216e5.
This reverts commit 9b8825b6.

I found that combining sweep and move is not safe.  I don't think that
we can do compaction concurrently with _anything_ unless there is a read
barrier installed.

Here is a simple example.  A class object is freed, and during it's free
step, it tries to remove itself from its parent's subclass list.
However, during the sweep step, the parent class was moved and the
"currently being freed" class didn't have references updated yet.  So we
get a segv like this:

```
(lldb) bt
* thread #1, name = 'ruby', stop reason = signal SIGSEGV
  * frame #0: 0x0000560763e344cb ruby`rb_st_lookup at st.c:320:43
    frame #1: 0x0000560763e344cb ruby`rb_st_lookup(tab=0x2f7469672f6e6f72, key=3809, value=0x0000560765bf2270) at st.c:1010
    frame #2: 0x0000560763e8f16a ruby`rb_search_class_path at variable.c:99:9
    frame #3: 0x0000560763e8f141 ruby`rb_search_class_path at variable.c:145
    frame #4: 0x0000560763e8f141 ruby`rb_search_class_path(klass=94589785585880) at variable.c:191
    frame #5: 0x0000560763ec744e ruby`rb_vm_bugreport at vm_dump.c:996:17
    frame #6: 0x0000560763f5b958 ruby`rb_bug_for_fatal_signal at error.c:675:5
    frame #7: 0x0000560763e27dad ruby`sigsegv(sig=<unavailable>, info=<unavailable>, ctx=<unavailable>) at signal.c:955:5
    frame #8: 0x00007f8b891d33c0 libpthread.so.0`___lldb_unnamed_symbol1$$libpthread.so.0 + 1
    frame #9: 0x0000560763efa8bb ruby`rb_class_remove_from_super_subclasses(klass=94589790314280) at class.c:93:56
    frame #10: 0x0000560763d10cb7 ruby`gc_sweep_step at gc.c:2674:2
    frame #11: 0x0000560763d1187b ruby`gc_sweep at gc.c:4540:2
    frame #12: 0x0000560763d101f0 ruby`gc_start at gc.c:6797:6
    frame #13: 0x0000560763d15153 ruby`rb_gc_compact at gc.c:7479:12
    frame #14: 0x0000560763eb4eb8 ruby`vm_exec_core at vm_insnhelper.c:5183:13
    frame #15: 0x0000560763ea9bae ruby`rb_vm_exec at vm.c:1953:22
    frame #16: 0x0000560763eac08d ruby`rb_yield at vm.c:1132:9
    frame #17: 0x0000560763edb4f2 ruby`rb_ary_collect at array.c:3186:9
    frame #18: 0x0000560763e9ee15 ruby`vm_call_cfunc_with_frame at vm_insnhelper.c:2575:12
    frame #19: 0x0000560763eb2e66 ruby`vm_exec_core at vm_insnhelper.c:4177:11
    frame #20: 0x0000560763ea9bae ruby`rb_vm_exec at vm.c:1953:22
    frame #21: 0x0000560763eac08d ruby`rb_yield at vm.c:1132:9
    frame #22: 0x0000560763edb4f2 ruby`rb_ary_collect at array.c:3186:9
    frame #23: 0x0000560763e9ee15 ruby`vm_call_cfunc_with_frame at vm_insnhelper.c:2575:12
    frame #24: 0x0000560763eb2e66 ruby`vm_exec_core at vm_insnhelper.c:4177:11
    frame #25: 0x0000560763ea9bae ruby`rb_vm_exec at vm.c:1953:22
    frame #26: 0x0000560763ceee01 ruby`rb_ec_exec_node(ec=0x0000560765afa530, n=0x0000560765b088e0) at eval.c:296:2
    frame #27: 0x0000560763cf3b7b ruby`ruby_run_node(n=0x0000560765b088e0) at eval.c:354:12
    frame #28: 0x0000560763cee4a3 ruby`main(argc=<unavailable>, argv=<unavailable>) at main.c:50:9
    frame #29: 0x00007f8b88e560b3 libc.so.6`__libc_start_main + 243
    frame #30: 0x0000560763cee4ee ruby`_start + 46
(lldb) f 9
frame #9: 0x0000560763efa8bb ruby`rb_class_remove_from_super_subclasses(klass=94589790314280) at class.c:93:56
   90
   91  		*RCLASS_EXT(klass)->parent_subclasses = entry->next;
   92  		if (entry->next) {
-> 93  		    RCLASS_EXT(entry->next->klass)->parent_subclasses = RCLASS_EXT(klass)->parent_subclasses;
   94  		}
   95  		xfree(entry);
   96  	    }
(lldb) command script import -r misc/lldb_cruby.py
lldb scripts for ruby has been installed.
(lldb) rp entry->next->klass
(struct RMoved) $1 = (flags = 30, destination = 94589792806680, next = 94589784369160)
(lldb)
```

Methods:

    #freeze
    #<<
    #push
    #pop
    #shift
    #unshift
    #slice
    #at
    #first
    #last

We don't need to resolve symbols when freeing cc tables, so this commit
just changes the id table iterator to look at values rather than keys
and values.

  We avoid to use the current delegate library under the Ruby 2.7.

https://github.com/ruby/fcntl/commit/39e0faedc5

https://github.com/ruby/dbm/commit/25a6f365bb

https://github.com/ruby/gdbm/commit/f42103fe93

Kernel#sleep should still return seconds slept, even when using a
Thread.scheduler. The return value of Scheduler#wait_sleep can be
ignored.

These test runners do not deal with `-n` make flag.

CI fails with GC while `foo{}`, so that disable GC for this script.

Added configuration for CodeQL scanning by GitHub

Now that vm_empty_cc is VM_CALLCACHE_UNMARKABLE, it has to be properly
ruled out from being GCed.

https://github.com/ruby/singleton/commit/b7c583f5cd

When on USE_EMBED_CI, cd is stored statically.  Previous use could cache
stale cd->cc, which could have already been GCed.  Need flush them.

Entires not GC-able must be considered to be volatile.  Not eligible for
later use.

It was a wrong idea to assume CIs are always embedded.

Ko1 prefers variables be assgined, instead of bare literals in function
arguments.

Seems they do not allow compound literals for static variables. See
https://github.com/ruby/ruby/runs/733735274

This further reduces the generated binary of vm_call_method from 566
bytes to 545 bytes on my machine, according to nm(1).

This changeset reduces the generated binary of rb_vm_call0 from 281
bytes to 211 bytes on my machine.  Should reduce GC pressure as well.

This changeset reduces the generated binary of vm_call_method from 600
bytes to 566 bytes on my machine, accroding to nm(1).

This changeset reduces the generated binary of vm_call_method_each_type
from 2,442 bytes to 2,378 bytes on my machine, accroding to nm(1).

This changeset reduces the generated binary of vm_call_method_each_type
from 2,522 bytes to 2,442 bytes on my machine, accroding to nm(1).

This changeset reduces the generated binary of
vm_call_method_missing_body from 604 bytes to 532 bytes on my machine.
Should reduce GC pressure as well.

This changeset reduces the generated binary of vm_call_symbol from 808
bytes to 798 bytes on my machine.  Should reduce GC pressure as well.

This changeset reduces the generated binary of vm_call_alias from 188
bytes to 149 bytes on my machine, accroding to nm(1).

This changeset reduces the generated binary of rb_eql_opt from 86 bytes to
20 bytes on my machine, according to nm(1).

Now that vm_empty_cc is statically allocated outside of the object
space.  It shall not be GCed.  Here, because vm_search_cc can return
that.  Must not be blindly passed to RB_OBJ_WRITE, unless assertions
fail on RGENGC_CHECK_MODE, like this:

-- C level backtrace information
-------------------------------------------
ruby(rb_print_backtrace+0x19) [0x5555557fd579] vm_dump.c:757
ruby(rb_vm_bugreport+0x151) [0x5555557fd6f1] vm_dump.c:955
ruby(rb_bug+0x1d6) [0x5555558d6396] error.c:660
ruby(check_rvalue_consistency_force+0x707) [0x5555555adb97] gc.c:1289
ruby(check_rvalue_consistency+0x1a) [0x555555598a0a] gc.c:1305
ruby(RVALUE_OLD_P+0x15) [0x5555555975d5] gc.c:1382
ruby(rb_gc_writebarrier+0x9f) [0x55555559753f] gc.c:6882
ruby(rb_obj_written+0x3a) [0x5555557a025a] include/ruby/internal/rgengc.h:180
ruby(rb_obj_write+0x41) [0x5555557a1a81] include/ruby/internal/rgengc.h:195
ruby(rb_vm_search_method_slowpath+0x5a) [0x5555557a125a] vm_insnhelper.c:1603
ruby(vm_search_method_fastpath+0x197) [0x5555557d8027] vm_insnhelper.c:1638
ruby(vm_search_method+0xea) [0x5555557d7d2a] vm_insnhelper.c:1650
ruby(vm_search_method_wrap+0x29) [0x5555557dbaf9] vm_insnhelper.c:4091
ruby(vm_sendish+0xa9) [0x5555557dba39] vm_insnhelper.c:4143
ruby(vm_exec_core+0xe357) [0x5555557b0757] insns.def:801
ruby(rb_vm_exec+0x12c) [0x5555557d17cc] vm.c:1942
ruby(invoke_block+0xea) [0x5555557f42fa] vm.c:1058
ruby(invoke_iseq_block_from_c+0x16e) [0x5555557f3eae] vm.c:1130
ruby(invoke_block_from_c_bh) vm.c:1148
ruby(vm_yield+0x71) [0x5555557f3c41] vm.c:1193
ruby(rb_yield_0+0x25) [0x5555557ca615] vm_eval.c:1141
ruby(rb_yield_1+0x27) [0x5555557ca5c7] vm_eval.c:1147
ruby(rb_yield+0x34) [0x5555557ca654] vm_eval.c:1157
ruby(rb_ary_collect+0xb0) [0x555555828320] array.c:3186
ruby(call_cfunc_0+0x29) [0x5555557f0f39] vm_insnhelper.c:2385
ruby(vm_call_cfunc_with_frame+0x278) [0x5555557eca98] vm_insnhelper.c:2553
ruby(vm_sendish+0xd0) [0x5555557dba60] vm_insnhelper.c:4146
ruby(vm_exec_core+0xe0f8) [0x5555557b04f8] insns.def:782
ruby(rb_vm_exec+0x12c) [0x5555557d17cc] vm.c:1942
ruby(invoke_block+0xea) [0x5555557f42fa] vm.c:1058
ruby(invoke_iseq_block_from_c+0x16e) [0x5555557f3eae] vm.c:1130
ruby(invoke_block_from_c_bh) vm.c:1148
ruby(vm_yield+0x71) [0x5555557f3c41] vm.c:1193
ruby(rb_yield_0+0x25) [0x5555557ca615] vm_eval.c:1141
ruby(rb_yield_1+0x27) [0x5555557ca5c7] vm_eval.c:1147
ruby(rb_yield+0x34) [0x5555557ca654] vm_eval.c:1157
ruby(rb_ary_each+0xa5) [0x55555581c795] array.c:2242
ruby(call_cfunc_0+0x29) [0x5555557f0f39] vm_insnhelper.c:2385
ruby(vm_call_cfunc_with_frame+0x278) [0x5555557eca98] vm_insnhelper.c:2553
ruby(vm_sendish+0xd0) [0x5555557dba60] vm_insnhelper.c:4146
ruby(vm_exec_core+0xe0f8) [0x5555557b04f8] insns.def:782
ruby(rb_vm_exec+0x12c) [0x5555557d17cc] vm.c:1942
ruby(invoke_block+0xea) [0x5555557f42fa] vm.c:1058
ruby(invoke_iseq_block_from_c+0x16e) [0x5555557f3eae] vm.c:1130
ruby(invoke_block_from_c_bh) vm.c:1148
ruby(vm_yield+0x71) [0x5555557f3c41] vm.c:1193
ruby(rb_yield_0+0x25) [0x5555557ca615] vm_eval.c:1141
ruby(rb_yield_1+0x27) [0x5555557ca5c7] vm_eval.c:1147
ruby(rb_yield+0x34) [0x5555557ca654] vm_eval.c:1157
ruby(rb_ary_each+0xa5) [0x55555581c795] array.c:2242
ruby(call_cfunc_0+0x29) [0x5555557f0f39] vm_insnhelper.c:2385
ruby(vm_call_cfunc_with_frame+0x278) [0x5555557eca98] vm_insnhelper.c:2553
ruby(vm_sendish+0xd0) [0x5555557dba60] vm_insnhelper.c:4146
ruby(vm_exec_core+0xe0f8) [0x5555557b04f8] insns.def:782
ruby(rb_vm_exec+0x19f) [0x5555557d183f] vm.c:1951
ruby(rb_iseq_eval+0x30) [0x5555557d2530] vm.c:2190
ruby(load_iseq_eval+0xd6) [0x5555555fa7e6] load.c:592
ruby(require_internal+0x25e) [0x5555555f7f5e] load.c:1022
ruby(rb_require_string+0x27) [0x5555555f74e7] load.c:1094
ruby(rb_f_require_relative+0x5f) [0x5555555f758f] load.c:837
ruby(call_cfunc_1+0x30) [0x5555557f0f70] vm_insnhelper.c:2391
ruby(vm_call_cfunc_with_frame+0x278) [0x5555557eca98] vm_insnhelper.c:2553
ruby(vm_call_cfunc+0xad) [0x5555557e521d] vm_insnhelper.c:2574
ruby(vm_call_method_each_type+0xc7) [0x5555557e4af7] vm_insnhelper.c:3040
ruby(vm_call_method+0x19c) [0x5555557e45dc] vm_insnhelper.c:3144
ruby(vm_call_general+0x2d) [0x5555557c8c3d] vm_insnhelper.c:3176
ruby(vm_sendish+0xd0) [0x5555557dba60] vm_insnhelper.c:4146
ruby(vm_exec_core+0xe357) [0x5555557b0757] insns.def:801
ruby(rb_vm_exec+0x12c) [0x5555557d17cc] vm.c:1942
ruby(rb_iseq_eval_main+0x30) [0x5555557d2670] vm.c:2201
ruby(rb_ec_exec_node+0x16b) [0x55555557e39b] eval.c:296
ruby(ruby_run_node+0x72) [0x55555557e1f2] eval.c:354
ruby(main+0x78) [0x55555557a5d8] main.c:50

This changeset reduces the generated binary of rb_equal_opt from 129 bytes
to 17 bytes on my machine, according to nm(1).

CIs are created on-the-fly, which increases GC pressure.  However they
include no references to other objects, and those on-the-fly CIs tend to
be short lived.  Why not skip allocation of them.  In doing so we need
to add a flag denotes the CI object does not reside inside of objspace.

This is such a hot path that it's worth eliminating a function call.  Use
the static variable directly instead.

For debug.  Must not change generated binary unless VM_ASSERT is on.