Update for recent changes to common submodule

This just replaces every "$ERROR_CFLAGS" usage with a usage of
"$WARNING_CFLAGS $ERROR_CFLAGS" to get the same functionality as
previously.

Actually using that separation will happen later.

configure.ac

@@ -173,7 +173,7 @@ fi
 AC_SUBST(DEPRECATED_CFLAGS)
 
 dnl every flag in GST_OPTION_CFLAGS can be overridden at make time
-GST_OPTION_CFLAGS="\$(ERROR_CFLAGS) \$(DEBUG_CFLAGS) \$(PROFILE_CFLAGS) \$(GCOV_CFLAGS) \$(OPT_CFLAGS) \$(DEPRECATED_CFLAGS)"
+GST_OPTION_CFLAGS="\$(WARNING_CFLAGS) \$(ERROR_CFLAGS) \$(DEBUG_CFLAGS) \$(PROFILE_CFLAGS) \$(GCOV_CFLAGS) \$(OPT_CFLAGS) \$(DEPRECATED_CFLAGS)"
 
 AC_SUBST(GST_OPTION_CFLAGS)