Backport MSan ASLR compatibility improvements

[thurstond]

Some distros have been increasing ASLR entropy e.g., Arch Linux (google/sanitizers#1716 (comment)) and Ubuntu 22.04LTS (actions/runner-images#9491). The latter change recently caused sanitizers on Github runners to fail, because their LLVM did not have the fix.

Most of the fixes for the sanitizers are already in llvm 18.1.0 or earlier (google/sanitizers#1614 (comment)); MSan is the most important of the sanitizers for which the fix is not already in a release. We would therefore like to backport the fix to LLVM 18; this won't immediately fix the Ubuntu issues, but it will help close the gap faster.

[thurstond]

/cherry-pick 58f7251 af2bf86

[llvmbot]

Failed to cherry-pick: 58f7251

https://github.com/llvm/llvm-project/actions/runs/8381979658

Please manually backport the fix and push it to your github fork. Once this is done, please create a pull request

[thurstond]

/cherry-pick af2bf86 58f7251

[llvmbot]

Failed to cherry-pick: 58f7251

https://github.com/llvm/llvm-project/actions/runs/8382008073

Please manually backport the fix and push it to your github fork. Once this is done, please create a pull request

[llvmbot]

/pull-request #86201