Marking external headers with -isystem is a common strategy for dealing
with warning suppression for files outside your control. This can be a
mistake as it can suppress warnings from misuse such as conversion in std::
optional, but such are the tradeoffs for false positives.
If module interfaces are built as part of a project do we need mechanisms
to suppress warnings? Standard libraries use pragmas to mark themselves,
but most libraries will and should not?

Thoughts raised due to
https://lucisqr.substack.com/p/the-warnings-you-never-saw -- which I have
issues with and have not completely verified.