[compiler-rt] [compiler-rt][msan] Add MSan support for Hexagon (Linux) (PR #189124)

[Thurston Dang via llvm-commits]

thurstond wrote:

> Once reviewers are satisfied, since this commit enables hexagon as `ALL_MSAN_SUPPORTED_ARCH`, I'll merge it only after the other fixes land: #189199 #189198 #189197.
```
        ___
       /   \
   ,--<  T  >--.
  /    \___/    \
  \ H  /   \ N  /
   >--<  A >--<
  /    \___/   \
  \ K  /   \ !  /
   `--<  S  >--'
       \___/
```

https://github.com/llvm/llvm-project/pull/189124