Fix for https://github.com/atgreen/libffi/issues/141
x86: Best guess at update for Darwin
x86: Disable .org for Darwin
x86: Use .balign not .align

The Apple assembler defaults to power of two alignment, rather than
byte alignment like everyone else.  Force byte alignment by using
the proper directive.
x86: Honor alignment of arguments

Darwin aligns long-double to 16, and thus all of the long double
tests were failing due to not honoring that.  We ought to be able
to devise a test case for GCC using __attribute__((aligned)) that
would have failed too.
x86: Remove use of .cfi_escape

The unwind info isn't 100% correct at all points during the epilogue,
and not annotating is just as incorrect as the annotation.  This works
better on systems that do not support DW_OP_call_frame_cfa.
x86: Avoid using gas local labels

Which are unsupported by Darwin cctools as.
Thankfully this doesn't uglify the source too much.
x86: Reinstate hand-written unwind info for unix64.S

One more try to get default Darwin to work.
x86: More Darwin unwind fixups

EHFrame{N} IIRC is a special cue to ld64 that it should treat the unwind
in the object as "special/legacy" .. [these days everything is .cfi_xxxx
(except, cctools-as, as you noted)] .. without that much confusion arises
with ld64's atom-isation of the eh_frame section.

xxxx.eh labels are not needed for darwin ld64 >= 85.2.1 (i.e. darwin9,
xcode 3.1.4) to all intents and purposes, that's all that matters now,
since I think that anyone trying to build on 10.4/darwin8/xcode2.5 would
have to use a later ld64 (from odcctools) for other reasons.
x86: Expand FFI_GO_CLOSURE

If we're going to have to hand-write unwind info for darwin,
these macros make the job harder.
x86: Fix some unwind errors
x86: Reinstate hand-written unwind info for sysv.S