Now that libtoolize requires an installed GNU M4 to parse
configure.ac and aclocal.m4 sources for libltdl macros, let the
user know at configure time when it is missing.
* m4/m4.m4: New file for rejecting non-GNU and buggy GNU versions
of M4. Copied from GNU Autoconf m4.m4.
* Makefile.am (lt_aclocal_m4_deps): Add m4/m4.m4.
* configure.ac (AC_PROG_GNU_M4): Call it.
* NEWS: Update.
Reported by Michael Felt
Signed-off-by: Gary V. Vaughan <gary@gnu.org>
