maint: share useful functions from general.m4sh.

maint: share useful functions from general.m4sh.

* build-aux/ltmain.m4sh (func_append, func_append_quoted)
(func_arith, func_len): Removed from here...
* build-aux/general.m4sh (func_append, func_append_quoted)
(func_arith, func_len): ...and added to here.
(func_dirname, func_dirname_and_basename, func_normal_abspath)
(func_relative_path): Use func_append.
* tests/getopt-m4sh.at (_LT_AT_FALLBACK_FUNC_EXTRACT): Removed.
Fallback functions are now in any m4sh generated file
automatically.

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