[compiler-rt] [libcxx] [libcxxabi] [lldb] [libc] [llvm] [flang] [clang] [lld] [clang-tools-extra] [libunwind] [PowerPC] Combine sub within setcc back to sext (PR #66978)

[Qiu Chaofan via llvm-commits]

https://github.com/ecnelises edited https://github.com/llvm/llvm-project/pull/66978