libtoolize: rename `libltdl/m4' directory to standard `m4'.

libtoolize: rename `libltdl/m4' directory to standard `m4'.

In addition to moving the autoconf macro directory into the
place expected by GNU developers ($top_srcdir/m4), we also
simplify libtoolize somewhat by having libltdl use whatever
directory was specified by the parent project.  This is much
more flexible, allows libltdl client projects to also use a
single canonical `$top_srcdir/m4' macro directory, and maintains
backward compatibility with existing projects that wish to
continue using $ltdl_dir/m4.
* libltdl/m4: Moved to it's parent directory.
* Makefile.am (ACLOCAL_AMFLAGS, BUILDCHECK_ENVIRONMENT)
(libltdl/Makefile.am, libltdl/aclocal.m4): Adjust.
* configure.ac (AC_CONFIG_MACRO_DIR): Adjust.
* libltdl/configure.ac (AC_CONFIG_MACRO_DIR): Remove. The
libtoolize script can pick up the project macro directory from
ACLOCAL_AMFLAGS in libltdl/Makefile.am, saving us from needing
to regenerate configure for the sake of a different macro
directory declared in the libltdl using client project.
* libtoolize.m4sh (func_install_pkgmacro_subproject): Remove.
(func_install_pkgmacro_parent): Remove.
(subproject_macro_dir): Remove.
(require_libltdl_Makefile_am, require_ltdl_aclocal_amflags)
(require_ltdl_am_macro_dir): New functions, generated at runtime
by adding libltdl/Makefile.am to the generation loop.
(func_install_pkgmacro_files): Considerably simplified now that
we have only a single macro directory to worry about.
(require_ltdl_relative_macro_dir): New function. Calculate the
relative path from $ltdl_dir to the parent project macro_dir.
(require_Makefile_am_filter): Depending on $ltdl_mode, edit
Makefile.am ACLOCAL_AMFLAGS to use the parent project macro
directory if necessary.
(require_aclocal_m4_filter): Make sure m4_includes point to the
correct macro directory by editing the file as it is copied
into the parent project.
(func_install_pkgltdl_files): Use the filters.
(func_check_macros): Remove various advice that no longer
applies with an always shared macro directory.
(func_require_ltdl_dir): Don't default ltdl_dir to subproject
when `--ltdl' was not given.
(func_require_ltdl_mode): Leave ltdl_mode empty when ltdl_dir is
not set.
(func_require_macro_dir): Default to $ltdl_dir/m4 in subproject
mode with no other directory implied by AC_CONFIG_MACRO_DIR or
ACLOCAL_AMFLAGS, otherwise m4 as before.
* tests/libtoolize.at: Match new "creating file `Makefile.am'"
messages correctly.
(subproject ltdl with non-shared directories): This test no
longer makes sense, so repurposed...
(subproject ltdl with non-canonical macro dir): ...this, to
ensure subproject ltdl continues to automatically share the
parent macro directory.
* tests/cdemo/Makefile.am, tests/demo/Makefile.am,
tests/depdemo/Makefile.am, tests/f77demo/Makefile.am,
tests/fcdemo/Makefile.am, tests/mdemo/Makefile.am,
tests/mdemo2/Makefile.am, tests/pdemo/Makefile.am,
tests/tagdemo/Makefile.am (ACLOCAL_AMFLAGS): Use new location
of macro_dir.
* NEWS: Updated.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>