[llvm-branch-commits] [sanitizer] Add TryMemCpy (PR #112668)

[Vitaly Buka via llvm-branch-commits]

https://github.com/vitalybuka created https://github.com/llvm/llvm-project/pull/112668

For posix implementation is similar to
`IsAccessibleMemoryRange`, using `pipe`.

We need this because we can't rely on non-atomic
`IsAccessibleMemoryRange` + `memcpy`, as the
protection or mapping may change and we may
crash.