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

[Rainer Orth via llvm-commits]

rorth wrote:

The test also breaks the [Solaris/amd64](https://lab.llvm.org/staging/#/builders/120/builds/12604) bot:

- `FAIL: Builtins-x86_64-sunos :: fixunstfdi_test.c`:
  ```
  Exit Code: 1

  Command Output (stdout):
  --
  error in __fixunstfdi(0X1.0000000000000000P+0) = 0, expected 1
  ```
- `FAIL: Builtins-x86_64-sunos :: multc3_test.c`:
  ```
  /var/llvm/tools/clang/stage2-bins/projects/compiler-rt/test/builtins/Unit/X86_64SunOSConfig/Output/multc3_test.c.script: line 1: 18353 Segmentation Fault
  ```

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