Adapt configure.exe to use qmake to do most of the work of configuring
Qt. This unifies a large part of our configuration system between Unix
and Windows. configure.exe is now still doing the license check,
creating qconfig.cpp, building qmake, and not much more.

On the way, re-implement the still missing Windows-specific tests with
the new system.

The opengles2 vs. opengl-desktop conditions got a bit convoluted, as
Unix prefers desktop GL, while Windows GLES2 (via ANGLE). Superficially,
there is a circular dependency, but the platform scopes are supposed to
break it.

Done-with: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>
Change-Id: Ia1941f2c34b7f5bd4990a7673cd737361381c2e7
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>