[libc] `process_mrelease` issue tracking

[SchrodingerZhu]

The following PR are initiation and fix attempts to the unstable hanging process_mrelease tests. #118049 should fix it but the buildbot of GPU is not entirely happy (it seems due to other reasons). If CI is still being unstable, all patches in the chain will be reverted.

#118049
#117956
#117951
#117851
#117807
#117503

[nickdesaulniers]

There's at least one flake

libc-x86_64-debian-fullbuild-dbg-asan has failed twice recently (not back to back)

https://lab.llvm.org/buildbot/#/builders/171/builds/11553/steps/4/logs/stdio
https://lab.llvm.org/buildbot/#/builders/171/builds/11547/steps/4/logs/stdio

FAILED: projects/libc/test/src/sys/mman/linux/CMakeFiles/libc.test.src.sys.mman.linux.process_mrelease_test /home/llvm-libc-buildbot/buildbot-worker/libc-x86_64-debian-fullbuild/libc-x86_64-debian-fullbuild-dbg-asan/build/projects/libc/test/src/sys/mman/linux/CMakeFiles/libc.test.src.sys.mman.linux.process_mrelease_test

[nickdesaulniers]

Sounds like there's a new PR here?