Visual Studio: Fix headers search path for Pango
Visual Studio: Fix headers search path for Pango

The test programs make use of Pango as well, so look for the Pango headers (as
well as the HarfBuzz headers, which are required by the Pango headers in the
recent releases) in the paths under $(PREFIX) as appropriate.

GNOME/librsvg,GNOME/librsvg,GNOME/librsvg,GNOME/librsvg