[compiler-rt] [compiler-rt][rtsan] NFC: Refactor context helper functions (PR #106869)

[Chris Apple via llvm-commits]

cjappl wrote:

Test failure is unrelated:

```
_bk;t=1725135284392FAIL: lld :: ELF/avr-reloc.s (83333 of 85610)

_bk;t=1725135284392******************** TEST 'lld :: ELF/avr-reloc.s' FAILED ********************

_bk;t=1725135284392Exit Code: 1

_bk;t=1725135284392

_bk;t=1725135284392Command Output (stderr):
```

https://github.com/llvm/llvm-project/pull/106869