Merge commit 9f85bc834b07 from llvm-project (by Nikita Popov):

[PPCMergeStringPool] Only replace constant once (#92996)

In #88846 I changed this code to use RAUW to perform the replacement
instead of manual updates -- but kept the outer loop, which means we try
to perform RAUW once per user. However, some of the users might be freed
by the RAUW operation, resulting in use-after-free.

The case where this happens is constant users where the replacement
might result in the destruction of the original constant.

Fixes https://github.com/llvm/llvm-project/issues/92991.

This fixes a possible crash when building crypto/openssh/sshkey.c for
PowerPC targets.

Reported by: cperciva
PR: 276104
MFC after: 3 days

Merge llvm-project release/18.x llvmorg-18.1.6-0-g1118c2e05e67

This updates llvm, clang, compiler-rt, libc++, libunwind, lld, lldb and
openmp to llvm-project release/18.x llvmorg-18.1.6-0-g1118c2e05e67.

PR: 276104
MFC after: 3 days

Merge llvm-project main llvmorg-18-init-15088-gd14ee76181fb

This updates llvm, clang, compiler-rt, libc++, libunwind, lld, lldb and
openmp to llvm-project main llvmorg-18-init-15088-gd14ee76181fb.

PR: 276104
MFC after: 1 month

Merge llvm-project main llvmorg-18-init-15088-gd14ee76181fb

This updates llvm, clang, compiler-rt, libc++, libunwind, lld, lldb and
openmp to llvm-project main llvmorg-18-init-15088-gd14ee76181fb.

PR: 276104
MFC after: 1 month