Generate gnulib's toplevel Makefile.in using automake

Generate gnulib's toplevel Makefile.in using automake

This is a lot simpler and as a side-effect this will correctly
regenerate import/Makefile and config.h during rebuilds if
necessary.

gnulib/ChangeLog:

2019-11-15  Christian Biesinger  <cbiesinger@google.com>

	* Makefile.am: New file.
	* Makefile.in: Replace with generated file.
	* aclocal-m4-deps.mk: Remove.
	* configure.ac: Use the foreign option for automake and specify
	the aclocal search path here.
	* update-gnulib.sh: Don't generate aclocal-m4-deps.mk anymore.
	Also don't specify the aclocal include path here, now that it
	is in configure.ac.

Change-Id: I6a2c4d41cf4f0e21d5c813197bad63ed5c08e408