Add missing headers causing compile errors on Linux

Don't build GL example at all on Linux
Add PolyVoxConfig.cmake file

library/include/PolyVoxCore/BlockVolumeIterator.inl

@@ -23,6 +23,7 @@ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 #include "Block.h"
 #include "BlockVolume.h"
 #include "Vector.h"
+#include "Region.h"
 #pragma endregion
 
 namespace PolyVox

library/include/PolyVoxCore/Utility.h

@@ -26,6 +26,8 @@ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 
 #include "PolyVoxForwardDeclarations.h"
 
+#include <cassert>
+
 namespace PolyVox
 {
 	POLYVOX_API uint8 logBase2(uint32 uInput);

library/include/PolyVoxCore/Vector.inl

@@ -22,6 +22,7 @@ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 #include <cassert>
 #include <cmath>
 #include <string>
+#include <cstring>
 
 namespace PolyVox
 {