[libcxx-commits] [libcxx] [libc++] Avoid constructing additional objects when using map::at (PR #157866)

[Louis Dionne via libcxx-commits]

================

----------------
ldionne wrote:

Not attached to this file: let's do the same optimization in `unordered_map`,in a followup.

https://github.com/llvm/llvm-project/pull/157866