We want to look for the gdk-pixbuf-2.0 package, and we should leave a space
between -ldwmapi and -lzlib1 when we enable Broadway.
Also copy the generated gdk-3.0.pc and gtk+-3.0.pc as gdk-win32-3.0.pc and
gtk+-win32-3.0.pc respectively, to be in-line with the autotools builds.
Generate .pc files for the package, so that it would be easier for
building introspection for packages that depend on GTK+. Also split
PythonPath into PythonPath and PythonPathX64 to facilitate the build of
introspection files, which need to have Python that is built with the
same ac=rchitecture where GTK+ is built.
Clean up the formatting and spacing a bit.
