Merge llvm-project release/13.x llvmorg-13.0.0-rc3-8-g08642a395f23
This updates llvm, clang, compiler-rt, libc++, libunwind, lld, lldb and
openmp to llvmorg-13.0.0-rc3-8-g08642a395f23.
PR: 258209
MFC after: 2 weeks
(cherry picked from commit 8c6f6c0c80f896f9c90b7833def615dcb0ce9244)