It is not used anymore besides internally by the proc/gdbserial
backend.

* delve now can be built to arm64-arch and running on linux-arm64 OS.
* arm64 general-purpose registers have completed.
* arm64 disasm has completed.
Co-authored-by: Ntykcd996 <tang.yuke@zte.com.cn>
Co-authored-by: Nhengwu0 <wu.heng@zte.com.cn>

Fixes #1493

The linux version of proc/native and proc/core contained largely
overlapping implementations of the register handling code, deduplicate
it by moving it into proc/linutil.

Refactors some code, adds a bunch of docstrings and just generally fixes
a bunch of linter complaints.

Fncall.go was written with the assumption that the object returned by
proc.Thread.Registers does not change after we call
proc.Thread.SetPC/etc.

This is true for the native backend but not for gdbserial. I had
anticipated this problem and introduced the Save/SavedRegisters
mechanism during the first implementation of fncall.go but that's
insufficient.

Instead:

1. clarify that the object returned by proc.Thread.Registers could
   change when the CPU registers are modified.
2. add a Copy method to Registers that returns a copy of the registers
   that are guaranteed not to change when the CPU registers change.
3. remove the Save/SavedRegisters mechanism.

This solution leaves us the option, in the future, to cache the output
of proc.(Thread).Registers, avoiding a system call every time it's
called.

Implements the function call injection protocol introduced in go 1.11
by https://go-review.googlesource.com/c/go/+/109699.

This is only the basic support, see TODO comments in pkg/proc/fncall.go
for a list of missing features.

Updates #119

Instead of only tracking a few cherrypicked registers in stack.go track
all DWARF registers.

This is needed for cgo code and for the locationlists emitted by go in
1.10:
* The debug_frame sections emitted by C compilers can not be used
  without tracking all registers
* the loclists emitted by go1.10 need all registers of a frame to be
  interpreted.

Updates #794

- moved target.Interface into proc as proc.Process
- rename proc.IThread to proc.Thread
- replaced interfaces DisassembleInfo, Continuable and
  EvalScopeConvertible with Process.
- removed superfluous Gdbserver prefix from types in the gdbserial
  backend.
- removed superfluous Core prefix from types in the core backend.

- move native backend to pkg/proc/native
- move gdbserver backend to pkg/proc/gdbserial
- move core dumps backend to pkg/proc/core

On Windows we can sometimes encounter threads stopped in locations for
which we do not have entries in debug_frame.
These cases seem to be due to calls to Windows API in the go runtime,
we can still produce a (partial) stack trace in this circumstance by
following frame pointers (starting with BP).
We still prefer debug_frame entries when available since go functions
do not have frame pointers before go1.8.

Adds ability to load x87, SSE and AVX registers.

Fixes #666

Fixes flakiness of TestCmdLineArgs.

Implements #368

proc.(*Thread).GetG: reading TLS memory directly for g address instead of modifying the executable code

* Remove half baked CallFn implementation.
* Cleanup whitespace
* Cleanup read/write mem functions