build: Make a selected set of compiler warnings into hard errors
build: Make a selected set of compiler warnings into hard errors

This set is copied from glib.  There are certain warnings that should
never, *ever* be seen in modern C programs.  A classic example is
-Wimplicit-function-declaration.

See
https://git.gnome.org/browse/glib/commit/?id=28b30caecb8d53c0d41e6a46ef9ba01d2f08e051
for a much more extensive rationale.

edynox/libdnf,rpm-software-management/libdnf,edynox/libdnf,kalev/libhif,rpm-software-management/libdnf,cgwalters/libhif,rpm-software-management/libhif,Conan-Kudo/libhif,Conan-Kudo/libhif,cgwalters/libhif,rpm-software-management/libhif,kalev/libhif,rpm-software-management/libdnf,edynox/libdnf,Conan-Kudo/libhif,rpm-software-management/libdnf,edynox/libdnf,juhp/libhif,rpm-software-management/libhif,Conan-Kudo/libhif,hughsie/libhif,hughsie/libhif,cgwalters/libhif,juhp/libhif,rpm-software-management/libhif,hughsie/libhif,cgwalters/libhif,hughsie/libhif