some of these definitions were just plain wrong, others based on
outdated ancient "non-64" versions of the kernel interface.

as much as possible has now been moved out of bits/*

these changes break abi (the old abi for these functions was wrong),
but since they were not working anyway it can hardly matter.

the basic idea is that the only things in alltypes.h should be types
that either vary from system to system (in practice, not just in
theoretical la-la land - this is the implementation so we choose what
constraints we want to impose on ports) or which are needed by
multiple system headers.

actually FLT_ROUNDS needs to expand to a static inline function that
obtains the current rounding mode and returns it, but that will be
added later with fenv.h stuff.

this was a hack leftover from testing before the initial
check-in to git.

instead of allocating a userspace structure for signal-based timers,
simply use the kernel timer id. we use the fact that thread pointers
will always be zero in the low bit (actually more) to encode integer
timerid values as pointers.

also, this change ensures that the timer_destroy syscall has completed
before the library timer_destroy function returns, in case it matters.

this mainly just caused bloat, but could corrupt errno if a 0-arg
syscall ever failed.

glibc made the ridiculous choice to use pass-by-register calling
convention for these functions, which is impossible to duplicate
directly on non-gcc compilers. instead, we use ugly asm to wrap and
convert the calling convention. presumably this works with every
compiler anyone could potentially want to use.

with this patch, the syscallN() functions are no longer needed; a
variadic syscall() macro allows syscalls with anywhere from 0 to 6
arguments to be made with a single macro name. also, manually casting
each non-integer argument with (long) is no longer necessary; the
casts are hidden in the macros.

some source files which depended on being able to define the old macro
SYSCALL_RETURNS_ERRNO have been modified to directly use __syscall()
instead of syscall(). references to SYSCALL_SIGSET_SIZE and SYSCALL_LL
have also been changed.

x86_64 has not been tested, and may need a follow-up commit to fix any
minor bugs/oversights.

this commit shuffles around the location of syscall definitions so
that we can make a syscall() library function with both SYS_* and
__NR_* style syscall names available to user applications, provides
the syscall() library function, and optimizes the code that performs
the actual inline syscalls in the library itself.

previously on i386 when built as PIC (shared library), syscalls were
incurring bus lock (lock prefix) overhead at entry and exit, due to
the way the ebx register was being loaded (xchg instruction with a
memory operand). now the xchg takes place between two registers.

further cleanup to arch/$(ARCH)/syscall.h is planned.

this commit is part of an effort to make more of busybox work
out-of-the-box.

after re-reading 2.2.2 of POSIX 2008, all of these are in the correct
reserved namespaces and do not need protection.

only the structures, not the functions from ucontext.h, are supported
at this point. the main goal of this commit is to make modern gcc with
dwarf2 unwinding build without errors.

honestly, it probably doesn't matter how we define these as long as
they have members with the right names to prevent errors while
compiling libgcc. the only time they will be used is for propagating
exceptions across signal-handler boundaries, which invokes undefined
behavior anyway. but as-is, they're probably correct and may be useful
to various low-level applications dealing with virtualization, jit
code generation, and so on...

this allows sys/types.h to provide the pthread types, as required by
POSIX. this design also facilitates forcing ABI-compatible sizes in
the arch-specific alltypes.h, while eliminating the need for
developers changing the internals of the pthread types to poke around
with arch-specific headers they may not be able to test.