[compiler-rt] [tsan] Refine fstat{,64} interceptors (PR #86625)

[via llvm-commits]

https://github.com/wangleiat approved this pull request.

Tested OK on LoongArch. Prior to this, the following errors will be prompted:
```
ThreadSanitizer:DEADLYSIGNAL
==752233==ERROR: ThreadSanitizer: SEGV on unknown address 0x000000000000 (pc 0x000000000000 bp 0x7ffffbdfe080 sp 0x7ffffbdfe010 T752233)
==752233==Hint: pc points to the zero page.
==752233==The signal is caused by a READ memory access.
==752233==Hint: address points to the zero page.
```
LGTM, except for code formatting.
Thanks.

https://github.com/llvm/llvm-project/pull/86625