Merge llvm-project release/18.x llvmorg-18.1.0-rc3-0-g6c90f8dd5463
This updates llvm, clang, compiler-rt, libc++, libunwind, lld, lldb and
openmp to llvm-project release/18.x llvmorg-18.1.0-rc3-0-g6c90f8dd5463.
PR: 276104
MFC after: 1 month
(cherry picked from commit 56727255ad47072ec2cc81b4ae728a099697b0e4)