x86: Fix STDCALL

Messed up STDCALL in the "Best Guess for Darwin" patch.
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.