maint: substitute static directory names.

maint: substitute static directory names.

By substituting just the directory name as passed to the macro,
aux_dir can be used with or without $srcdir prefix, which is
more flexible, and always means the same thing in each file,
rather than sometimes being a directory name, sometimes relative
to $top_srcdir.
* configure.ac (AC_CONFIG_AUX_DIR, AC_CONFIG_MACRO_DIR)
(LT_CONFIG_LTDL_DIR): Don't force config.status substitutions
with unexpanded shell variables.
* Makefile.am, tests/defs.m4sh: Adjust.

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