Fix for missing wglext.h

[Devin Stone]

Just an FYI for everyone:

I ran into a problem building Polycode where the compiler would complain about not finding wglext.h. It was resolved by copying this file from Polycode-master\dependencies\downloads\ to Polycode-master\Release\Windows\Framework\Core\Dependencies\include\GL\

Ivan - I think this may be due to a problem somewhere in the glext cmakelists.txt. I didn't see anyone else posting about it though, so maybe it's a fluke.

-Devin