[compiler-rt] [compiler-rt][ubsan][nfc-ish] Fix a type conversion bug (PR #100665)

[Alan Zhao via llvm-commits]

alanzhao1 wrote:

> @alanzhao1 Actually, the spec for `ptrauth_sign` is:
> 
> ```
>    The result will have the same type as the original value.
> ```
> 
> So, I think we'd also fix the inline asm version while here. How about the following:
> 
> ```
>       __typeof(__value) ret;                \
> ```
> 
> ?

Done

https://github.com/llvm/llvm-project/pull/100665