[sanitizer][test] Fix FastUnwindTest on LoongArch

Fixes the `FastUnwindTest` unit test for LoongArch.
This change is similar to RISCV D90574.

The following test cases pass after applying the patch:
```
$ ./runtimes/runtimes-bins/compiler-rt/lib/sanitizer_common/tests/Sanitizer-loongarch64-Test
...
[  FAILED  ] FastUnwindTest.Basic
[  FAILED  ] FastUnwindTest.FramePointerLoop
[  FAILED  ] FastUnwindTest.MisalignedFramePointer
[  FAILED  ] FastUnwindTest.FPBelowPrevFP
[  FAILED  ] FastUnwindTest.CloseToZeroFrame
```

Reviewed By: SixWeining, xen0n, MaskRay

Differential Revision: https://reviews.llvm.org/D137314