[clang] [clang-tools-extra] [libcxx] [clang][Sema] Add -Wsuspicious-memcmp for memcmp on types without unique object representations (PR #214218)

[Aditya Medhane via cfe-commits]

https://github.com/flash1729 ready_for_review https://github.com/llvm/llvm-project/pull/214218