Visual Studio Builds: Fix gdkconfig.h Generation

...for Broadway builds, as it was producing a wrongly-named check file for
that configuration, so that a clean would not be correctly performed and
subsequently affected rebuilds.
GL: Fix typo in gdk_gl_texture_from_surface

Got a sign wrong in commit 800c712738f5666937e32d9f8cb32353513b9423
Updated POTFILES.in