fix compile error introduced in rev. 51773: missing header include.

Reported on IRC.

source/blender/blenkernel/BKE_DerivedMesh.h

@@ -75,6 +75,9 @@
 #include "BKE_customdata.h"
 #include "BKE_bvhutils.h"
 
+/* defines BLI_INLINE */
+#include "BLI_utildefines.h"
+
 struct CCGElem;
 struct CCGKey;
 struct MVert;