add includes to dsc.h to fix errors in it's own context (not real errors since dsc.h isnt compiled by itself, just screws up the code model in QtCreator without them)

src/dsc.h

@@ -7,6 +7,9 @@
 #ifndef __DSC_H
 #define __DSC_H
 
+#include <cstddef>
+#include "solvespace.h"
+
 class Vector;
 class Vector4;
 class Point2d;