configury: move autoconf macros to build-aux subdirectory. * ltdl/m4: Move from here... * build-aux/m4: ...to here. * configure.ac (AC_CONFIG_MACRO_DIR): Adjust. * Makefile.am (config_macro_dir, ACLOCAL_AMFLAGS): Adjust. * build-aux/m4/gnulib-cache.m4: Regenerate. Signed-off-by: Gary V. Vaughan <gary@gnu.org>