gnome3.gcr: propagate pkg-config dependencies

The pinentry_gnome package requires gcr. Unfortunately, when configure
asks about the library (or `pkg-config --libs gcr-base-3` is used) it
fails because glib is not in scope.

```
$ pkg-config --libs gcr-base-3
Package glib-2.0 was not found in the pkg-config search path.
Perhaps you should add the directory containing `glib-2.0.pc'
to the PKG_CONFIG_PATH environment variable
Package 'glib-2.0', required by 'gcr-base-3', not found
```

This commit moves glib and gtk to `propagatedBuildInputs` so pkgconfig
could find them.

See also 38b58bab