wrlib: Fixed and improved NETPBM examples

The tests examples were not compiling because of a missing X11 lib.

Signed-off-by: Carlos R. Mafra <crmafra@gmail.com>

wrlib/tests/testdraw.c

@@ -562,6 +562,8 @@ int main(int argc, char **argv)
 	RContextAttributes attr;
 	int visualID = -1;
 
+	(void) argc;
+
 	ProgName = strrchr(argv[0], '/');
 	if (!ProgName)
 		ProgName = argv[0];