glib-compile-resources: generate .d-file style dependency output for build tools

Add --dependency-file=foo.d option to generate a gcc -M -MF style
dependency file for other build tools. The current output of
--generate-dependencies is only useful for use directly in Makefile
rules, but can't be used in other build systems like that.

The generated dependency file looks like this:
$ glib-compile-resources --sourcedir= test.gresource.xml --dependency-file=-
test.gresource.xml: test1.txt test2.txt test2.txt

test1.txt:

test2.txt:

test2.txt:

Unlike --generate-dependencies, the --dependency-file option can be
used together with other --generate options to create dependencies
as side-effect of generating sources.

Based on a patch by Tim-Philipp Müller.

https://bugzilla.gnome.org/show_bug.cgi?id=745754

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

@@ -124,6 +124,9 @@ test.gresource: test.gresource.xml $(shell $(GLIB_COMPILE_RESOURCES) --generate-
 </programlisting>
 Note that this may or may not be portable to non-GNU <command>make</command>.
 </para>
+<para>
+Also see <option>--dependency-file</option>.
+</para>
 </listitem>
 </varlistentry>
 
@@ -160,6 +163,17 @@ which is what <option>--internal</option> does.
 </para></listitem>
 </varlistentry>
 
+<varlistentry>
+<term><option>--dependency-file=<replaceable>FILE</replaceable></option></term>
+<listitem><para>
+Write dependencies in the same style as gcc -M -MF to the given file.
+If <option>FILE</option> is -, the dependencies are written to the standard
+output. Unlike <option>--generate-dependencies</option>, this option can be
+combined with other <option>--generate</option> options to generate dependencies
+as a side-effect of generating sources.
+</para></listitem>
+</varlistentry>
+
 </variablelist>
 </refsect1>