Are there decent 'lint' or 'valgrind'-style tools for warning about use of nonportable APIs (or APIs without universal behavior)? I could imagine such a thing being immensely useful for those of us who write software and care.
A 'lint'-style tool would obviously be a static analysis thing. A 'valgrind'-style might be able to spot uses of various calls without POSIXLY_CORRECT defined.
Of course, not all warnings are meaningful for a program. Not all platform targets are meaningful for a program. It'd be a matter of defining the testing scope, as with anything else.