[compiler-rt] Sanitizer/MIPS: fix build fail on pre-R6 (PR #76894)

[Fangrui Song via llvm-commits]

MaskRay wrote:

I remember that I left a detailed alternative description on Phabricator but read-only mirror does not contain the latest comment...

The description should include some information about how the interceptor symbols work on mips. For example, on x86 it's:
```
malloc:
__interceptor_trampoline_malloc:
  jmp __interceptor_malloc

__interceptor_malloc:
___interceptor_malloc:
  // sanitizer interceptor implementation
```

https://maskray.me/blog/2023-01-08-all-about-sanitizer-interceptors contains some notes about the interceptor mechanism.


https://github.com/llvm/llvm-project/pull/76894