wcap: Add GCC_CFLAGS and fix more compiler warnings
diff --git a/wcap/main.c b/wcap/main.c
index 09e0aa7..466030e 100644
--- a/wcap/main.c
+++ b/wcap/main.c
@@ -30,6 +30,7 @@
 #include <unistd.h>
 #include <string.h>
 #include <fcntl.h>
+#include <assert.h>
 
 #include <cairo.h>
 
@@ -65,6 +66,8 @@
 		g = (p >> 8) & 0xff;
 		b = (p >> 16) & 0xff;
 		break;
+	default:
+		assert(0);
 	}
 
 	y = (19595 * r + 38469 * g + 7472 * b) >> 16;