libffi on 32-bit x86 now supports closures for all supported ABIs.
Thus, rewrite the last remaining duplicated-by-ABI test (closure_stdcall
and closure_thiscall) to use the generic ABI_NUM/ABI_ATTR mechanism.
The trampoline size is part of the ABI, so it cannot change. Move the
logic from the stdcall and thiscall trampolines to the functions they
call, to reduce them both to 10 bytes.
This drops the previously added support for raw THISCALL closures on
non-Windows. (Non-raw THISCALL closures still work.)
When sizeof(size_t) != sizeof(unsigned), adding a size_t to cif->bytes
produces a "possible loss of data" warning. However, the size_t in
question refers to the size of a single parameter. Use a cast to avoid
the warning.
Linux supports the stdcall calling convention, either via functions
explicitly declared with the stdcall attribute, or via code compiled
with -mrtd which effectively makes stdcall the default.
This introduces FFI_STDCALL, FFI_THISCALL, and FFI_FASTCALL on
non-Windows x86-32 platforms, as non-default calling conventions.
