Add missing include on sys/types.h to fix build on Musl libc

I guess sys/types.h is implicitely included on glibc but that's definitely
not the case on Musl libc. The include is however necessary to define
dev_t introduced in 3c82d5a919

src/core/drmdevice.h

@@ -9,6 +9,7 @@
 #pragma once
 
 #include <QString>
+#include <sys/types.h>
 
 #include "graphicsbufferallocator.h"
 #include "kwin_export.h"