-Wnoexcept-type under GCC triggers false positives if a nothrow function is called through a template argument.
See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80985 for details.
Several low-level constructs in LLVM take predicates by template-arg and the warning appears to be triggered by
all GNU libc character classification functions, for example.
The LLVM libraries have no stable C++ API, so the warning is not useful.