[compiler-rt] [compiler-rt][AArch64][FMV] Use the hw.optional.arm.caps fast path (PR #95275)

[Saagar Jha via llvm-commits]

saagarjha wrote:

Note that `CAP_BIT_FEAT_SME`/`CAP_BIT_FEAT_SME2`/`CAP_BIT_FEAT_SME_F64F64`/`CAP_BIT_FEAT_SME_I16I64` are still stripped out of the public SDK, which breaks the build of compiler-rt :( I've filed FB13964283 to get those added but until then I'd also check for e.g. `CAP_BIT_FEAT_SME` before trying to use these.

https://github.com/llvm/llvm-project/pull/95275