[platforms/drm] include missing errno.h include

CCMAIL: Xaver Hugl <xaver.hugl@gmail.com>

src/plugins/platforms/drm/drm_gpu.cpp

@@ -24,6 +24,7 @@
 #endif
 // system
 #include <algorithm>
+#include <errno.h>
 #include <unistd.h>
 // drm
 #include <xf86drm.h>