[compiler-rt] [SPARC][builtins] Add sparcv9 arch name for 32-bit SPARC (PR #170133)

[via llvm-commits]

koachan wrote:

> ```
> Builtins-sparc-sunos :: divtc3_test.c
> Builtins-sparc-sunos :: multc3_test.c
> ```
> Even for the 2-stage build, the two FAILing tests die with SIGILL

>From a cursory look this seems like a genuine case of ABI mismatch bug; the caller expects an sret return but the callee returns the value in the register. Will look into it, thanks!

For the rest...
Over here it turns out with or without this patch only the SIGILL ones failed too, so this might as well isn't needed.
If so then I'll close or rework this PR to fix the SIGILL tests for the time being at least (?)

https://github.com/llvm/llvm-project/pull/170133