[compiler-rt] [compiler-rt] Fix test ifdefs and XFAILs (PR #160687)

[Akira Hatanaka via llvm-commits]

ahatanak wrote:

The signature of the function declared in the test file is different from the builtin's signature.

declaration in the test: `long double _Complex __multc3(long double __a, long double __b, long double __c, long double __d);`
builtin: `Qcomplex __multc3(fp_t a, fp_t b, fp_t c, fp_t d)`.

I think we should skip the test if the return type or the argument types don't match.

https://github.com/llvm/llvm-project/pull/160687