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.