Install pkg-config metadata in multiarch location

This should be sufficient to make *some* dependent packages
cross-compile. Packages that need to run gimptool-2.0 during build
will still not cross-compile, unless they are able to run
host-architecture executables, for example via qemu.

Thanks: Helmut Grohne
Closes: #872424

debian/libgimp2.0-dev.install

@@ -1,5 +1,5 @@
 usr/lib/*.so
-usr/lib/pkgconfig/
+usr/lib/pkgconfig/*.pc usr/lib/${DEB_HOST_MULTIARCH}/pkgconfig
 usr/share/man/man1/gimptool-?.?.1
 usr/share/aclocal/gimp-?.?.m4
 usr/include/