Hello, here is a patch implementing the --gnu-make option for
gnulib-tool.py. Sorry in advance for the long ChangeLong entry. It
makes it look like I did work than I actually did :). All of these
commits were grouped together and were similar so I felt like it
didn't make too much sense to handle them separately.

I ended up testing these changes with Paul Eggert's merge-gnulib
script used by Emacs [1]. Maybe there is a better way to test it but
this seemed to work pretty well. First I would update the sources with
the regular gnulib-tool, save the generated Makefile, and then run the
script again with gnulib-tool.py.

cd /path/to/src/emacs/
./admin/merge-gnulib
mv lib/gnulib.mk.in lib/gnulib.mk.in.old
sed -i -e 's/gnulib-tool /gnulib-tool.py /g' admin/merge-gnulib
./admin/merge-gnulib
diff lib/gnulib.mk.in lib/gnulib.mk.in.old

The output seems to be correct. It isn't perfect but you can see what
parts still need to be implemented. For example, a lot of the variables
are named incorrectly because of the commit
415fae8ddcb39d33f364c81b0f199e28c65bb539 which is marked in
gnulib-tool.py.TODO.

-ifneq (,$(gl_GNULIB_ENABLED_euidaccess_CONDITION))
-ifneq (,$(GL_COND_OBJ_EUIDACCESS_CONDITION))
+ifneq (,$(gl_GNULIB_ENABLED_euidaccess))
+ifneq (,$(GL_COND_OBJ_EUIDACCESS))

Most of the other incorrect lines are because of the changes made to
generating header files which gnulib-tool.py has not caught up with.

Let me know if you see something that I missed.

Thanks,
Collin

[1] https://git.savannah.gnu.org/cgit/emacs.git/tree/admin/merge-gnulib