libcheck: Update the compatibility code and checks

libcheck: Update the compatibility code and checks

This brings us up-to-speed with the latest compatibility code from upstream
check git. For completeness, we do all the checks that upstream check does, but
we skip the snprintf/vsnprintf code because it's not straightforward (involves
running code and that is bad for cross-compilation) and not necessary for the
platforms we support anyway.

If someone really wants this, they can uncomment this and copy the relevant
checks from the check git repository.

https://bugzilla.gnome.org/show_bug.cgi?id=775870