Improve the include situation

Slightly clean up header inclusion with the help of clang's module system.
It's better for files to include the things you need directly.

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

src/vsync.c

@@ -19,6 +19,7 @@
 #include <sys/ioctl.h>
 #endif
 
+#include "config.h"
 #include "vsync.h"
 
 #ifdef CONFIG_VSYNC_DRM