zig clang -emit-llvm does not work as intended with assembly and is not available in compile step

[RossComputerGuy]

Zig Version

0.11.0-dev.1969+d525ecb52

Steps to Reproduce and Observed Behavior

Try compiling src/x86/unix64.S with zig clang in libffi, I have it integrated into my project and I discovered this error:

/home/ross/ExpidusOS/neutron/vendor/libs/libffi/src/x86/unix64.S:596:14: error: invalid variant 'rel'
 .long .LUW0@rel
             ^
/home/ross/ExpidusOS/neutron/vendor/libs/libffi/src/x86/unix64.S:615:14: error: invalid variant 'rel'
 .long .LUW5@rel
             ^
/home/ross/ExpidusOS/neutron/vendor/libs/libffi/src/x86/unix64.S:628:14: error: invalid variant 'rel'
 .long .LUW8@rel
             ^
/home/ross/ExpidusOS/neutron/vendor/libs/libffi/src/x86/unix64.S:642:15: error: invalid variant 'rel'
 .long .LUW12@rel
              ^
/home/ross/ExpidusOS/neutron/vendor/libs/libffi/src/x86/unix64.S:655:15: error: invalid variant 'rel'
 .long .LUW15@rel

I did some digging and -emit-llvm should fix that. I naturally tried emit_llvm_ir and emit_llvm_br in std.Build.CompileStep on one made from std.Build.addAssembly(). This however, does not solve this error. I noticed emit_llvm_ir and emit_llvm_br did not add the argument so I ran the command that was outputted with zig build --verbose-cc and it worked just fine. So we've got 2 problems here:

1. Currently, std.Build does not have a way to pass emit-llvm to zig clang
2. zig clang's -emit-llvm argument does not function the same as clang's -emit-llvm

Expected Behavior

What we should have is:

1. std.Build.CompileStep should pass -emit-llvm, probably with a new EmitOption called emit_llvm, which is passed to zig clang
2. zig clang -emit-llvm should be functioning the same as clang -emit-llvm which would fix the assembly error

[andrewrk]

Related: #14971

[RossComputerGuy]

This problem is kinda solved in libffi with defining HAVE_AS_X86_PCREL in the config file but on x86 (not x86_64), I run into #7935

[andrewrk]

zig clang is not a supported feature. Are you intending to use zig cc instead?

Closing since zig clang is unsupported. Will re-open if further information is provided.