On my Ubuntu system the GTK code fails to build :-
------------
ERROR: Build failed for target 'default (exploded-image)' in configuration 'linux-x86_64-normal-server-release' (exit code 2)
=== Output from failing command(s) repeated here ===
* For target support_native_java.desktop_libawt_xawt_gtk3_interface.o:
/home/prrace/jdk9-client/jdk/src/java.desktop/unix/native/libawt_xawt/awt/gtk3_interface.c: In function ‘get_integer_property’:
/home/prrace/jdk9-client/jdk/src/java.desktop/unix/native/libawt_xawt/awt/gtk3_interface.c:2550:19: error: initialization makes integer from pointer without a cast [-Werror]
/home/prrace/jdk9-client/jdk/src/java.desktop/unix/native/libawt_xawt/awt/gtk3_interface.c: In function ‘get_boolean_property’:
/home/prrace/jdk9-client/jdk/src/java.desktop/unix/native/libawt_xawt/awt/gtk3_interface.c:2557:19: error: initialization makes integer from pointer without a cast [-Werror]
cc1: all warnings being treated as errors
=== End of repeated output ===
------

It is due to this usage
gint intval = NULL;
I had pointed this out during the review process and asked
that it be fixed but it appears it was not.

It was noted that some other file already does this but the
difference is the include file sequence.

It appears NULL is being #defined to (void*)0 in this case for me
and some different include sequence in the other file is (I suppose) causing it to be #defined (0) in my case.

There is no reason not to make this change and it makes the
annoying build problem go away. Without this being fixed I always need
to disable-warnings-as-errors.