Qt5.4: Indicate that MinGW package is OpenGL

Change-Id: I9eac3a965ff8c5007dd636818f3c361c1454f3b3
Task-number: QTBUG-39050
Reviewed-by: Andrew Knight <andrew.knight@theqtcompany.com>
Reviewed-by: Kai Koehne <kai.koehne@theqtcompany.com>