Dispatch entries updates for Windows default build

The following commit adds two new functions to dynamic dispatch entries, glActiveTexture and glBlendFuncSeparate that aren't available on Windows by default (OpenGL 1.2). It also fixes a variable declaration to the begin of the scope for C89 compliance.

I don't have a Linux box at the moment for testing but I believe the changes are non breaking for other platforms, please let me know if any additional issues arise.