[libc++][multimap] Applied `[[nodiscard]]`#171644

frederick-vs-ja merged 2 commits intollvm:mainllvm/llvm-project:mainfrom

H-G-Hristov:hgh/libcxx/nodiscard-to-multimapH-G-Hristov/llvm-project:hgh/libcxx/nodiscard-to-multimapCopy head branch name to clipboard