[clang] [ARM][clang] Add some build attributes support (PR #161106)

[via cfe-commits]

paperchalice wrote:

> With this in mind I get: (ffp-model=precise ; default) clang --target=arm-none-eabihf -mcpu=cortex-a53 -mfloat-abi=hard -S -o - file.c -emit-llvm -ffp-model=precise | grep eabi
> 
> > !2 = !{i32 2, !"arm-eabi-fp-denormal", i32 1}
> > !3 = !{i32 2, !"arm-eabi-fp-exceptions", i32 1}
> > !4 = !{i32 2, !"arm-eabi-fp-number-model", i32 3}
> 
> (ffp-model=strict) clang --target=arm-none-eabihf -mcpu=cortex-a53 -mfloat-abi=hard -S -o - file.c -emit-llvm -ffp-model=strict | grep eabi
> 
> > !2 = !{i32 2, !"arm-eabi-fp-denormal", i32 1}
> > !3 = !{i32 2, !"arm-eabi-fp-number-model", i32 3}
> 

When testing with `-ffp-model=strict`, clang emits `warning: overriding currently unsupported use of floating point exceptions on this target` and sets exception model to `ignore` forcely.


https://github.com/llvm/llvm-project/pull/161106