[roll] Roll llvm-project/libc c6dea2e..93a49ab (7 commits)

93a49ab:https://llvm.googlesource.com/llvm-project/libc/+/93a49ab2597815420f0df5acf19b3f6c4aca293c [libc][stdlib] Avoid scanning values during environment lookup (#228633)
e350d86:https://llvm.googlesource.com/llvm-project/libc/+/e350d86052f0e35ed1905dbbfd63d6f22bf75ee9 Replace python 3.9 dict | operator to support older python versions (#236599)
9c1be75:https://llvm.googlesource.com/llvm-project/libc/+/9c1be75c1405d0a3c633ad4bb8c45f5047d19b30 [libc] Clean up redundant libc_errno includes and dependencies. (#237273)
e36a796:https://llvm.googlesource.com/llvm-project/libc/+/e36a79692f70f336c0901bf195b0cbe80f8b811c [libc] Add a placeholder for POSIX sys/shm.h header (#237283)
2a1646e:https://llvm.googlesource.com/llvm-project/libc/+/2a1646e9ac93983451e267b2e883980f53436761 [libc] Add truncation casts to avoid warnings in `file_test.cpp` (#237262)
f45418c:https://llvm.googlesource.com/llvm-project/libc/+/f45418c4725924f20b05de08d3479c112839bcf0 [libc] Fix uninitialized variable warning in FrexpTest.h (#237263)
52b67d4:https://llvm.googlesource.com/llvm-project/libc/+/52b67d4d47e72e9e155cb8add5e6524f216ec01c [libc] Clean up libc_errno implementation, dependencies, and add __errno_location alias (#235421)

Rolled-Repo: https://llvm.googlesource.com/llvm-project/libc
Rolled-Commits: c6dea2e632eb54..93a49ab2597815
Roller-URL: https://cr-buildbucket.appspot.com/build/8666431281390742209
CQ-Do-Not-Cancel-Tryjobs: true
Cq-Include-Trybots: luci.turquoise.global.try:run-postsubmit-tryjobs
Change-Id: I3837240f43528a6eb76d1e42bc0fc0e9ec2af458
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1937735
Commit-Queue: global-integration-roller@fuchsia-infra.iam.gserviceaccount.com <global-integration-roller@fuchsia-infra.iam.gserviceaccount.com>