glib-compile-resources: Add --generate-phony-targets flag

This includes phony targets for each dependency in the the generated
dependency file which allows building with `ninja` which doesn't like
the phony targets[1] but also allows silencing `make` errors similar to
gcc's -MP option.

[1] - https://github.com/ninja-build/ninja/issues/1184

https://bugzilla.gnome.org/show_bug.cgi?id=774368

docs/reference/gio/glib-compile-resources.xml

@@ -181,6 +181,15 @@ as a side-effect of generating sources.
 </para></listitem>
 </varlistentry>
 
+<varlistentry>
+<term><option>--generate-phony-targets</option></term>
+<listitem><para>
+When creating a dependency file with <option>--dependency-file</option>
+include phony targets in the same style as gcc -MP. This would typically
+be used with <literal>make</literal>.
+</para></listitem>
+</varlistentry>
+
 </variablelist>
 </refsect1>