Fixes for nodiscard std::optional, std::set operations

libc++ recently added more nodiscard attributes:
http://github.com/llvm/llvm-project/pull/169982 and
http://github.com/llvm/llvm-project/pull/170045

Bug: 468205004
Change-Id: Ie199d266b349696515e17bf8735333a202134f51
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7256034
Owners-Override: Nico Weber <[email protected]>
Reviewed-by: Nico Weber <[email protected]>
Auto-Submit: Hans Wennborg <[email protected]>
Commit-Queue: Hans Wennborg <[email protected]>
Commit-Queue: Nico Weber <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1557956}
NOKEYCHECK=True
GitOrigin-RevId: 54f527e0399c84e1d70fdeb17b4fa8d53b4bf8f3
1 file changed