gstqmlgl: open32.lib required for MinGW builds as well

Hi,

I'm using a MinGW build of gstreamer on Windows and I need the QML GL sink. After some searching I found out that it has to be built manually. There is an unresolved linker symbol regarding OpenGL functions though. It was fixed for MSVC builds but it has to be done for the MinGW compiler too.

UPD: I found the instructions on MRs and will submit it, thx