If we're using the system glib library then we need to make sure not to
include headers under deps/glib otherwise we end up with with
incompatible typedefs that break the build.
Reviewed-by: Neil Roberts <neil@linux.intel.com>
(cherry picked from commit 5d5fc97b59951ec56a4193b7ee7909ebd3cfbb94)
ab72a2275f