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
(cherry picked from commit 3a0793336edfc21cb6d4c8c5c5d7f1665f3e6c5a)