ffi_prep_cif_core had a special case for X86_WIN32, checking for
FFI_THISCALL in addition to the FFI_FIRST_ABI-to-FFI_LAST_ABI range
before returning FFI_BAD_ABI. However, on X86_WIN32, FFI_THISCALL
already falls in that range, making the special case unnecessary.
Remove it.
code, and makes it possible to link code compiled with different
options to those used to compile libffi. For example, a
-mlong-double-128 libffi can be used with -mlong-double-64 code.
Using the return value area as a place to pass parameters wasn't such
a good idea, causing a failure of cls_ulonglong.c. I didn't see this
when running the mainline gcc libffi testsuite because that version of
the test is inferior to the upstreamm libffi test.
Using NUM_FPR_ARG_REGISTERS rather than NUM_FPR_ARG_REGISTERS64 meant
that a parameter save area could be allocated before it was strictly
necessary. Wrong but harmless. Found when splitting apart ffi.c
into 32-bit and 64-bit support.
