Non-default ABIs aren't supported

[sadlerap]

The following function miscompiles:

#[no_mangle]
extern "efiapi" fn efi(x: u32, y: u32) -> u32 {
    x * y
}

LLVM emits this:

efi:
        mov     eax, ecx
        imul    eax, edx
        ret

GCC emits this (notice the incorrect registers used for parameters):

efi:
        mov     eax, edi
        imul    eax, esi
        ret

As far as I can tell, we don't preserve the declared ABI since libgccjit doesn't have a way to annotate the ABI of functions with an annotated ABI. This needs to be implemented for ui/asm/x86_64/multiple-clobber-abi.rs to pass, which requires both the sysv64 and win64 extern abi to be supported.

[antoyo]

Yeah, for that, we would need to support a few new function attributes. If you want to take a look, you would need to add the attributes in a few places:

• https://github.com/antoyo/gcc/blob/8e0113788aca4824e39acbc85237ab275075835d/gcc/jit/libgccjit.h#L2111
• https://github.com/antoyo/gcc/blob/8e0113788aca4824e39acbc85237ab275075835d/gcc/jit/jit-recording.cc#L4822
• https://github.com/antoyo/gcc/blob/8e0113788aca4824e39acbc85237ab275075835d/gcc/jit/jit-playback.cc#L523