Fixed finding MinGW symbols; checked the desugared type when visiting pointer types.

Added an option for the used ABI to the C++ Parser class.
The desugared check fixes an exception when wrapping

void glMultiDrawElementsIndirectAMD(GLenum mode, GLenum type, const GLvoid *indirect, GLsizei primcount, GLsizei stride);

in qopenglextensions.h.