libtool 2.4: questionable advice

[Bruno Haible]

Hi,

Can someone explain to me this advice from libtool 2.4? It says

  libtoolize: Consider adding `AC_CONFIG_MACRO_DIR([m4])' to configure.ac and
  libtoolize: rerunning libtoolize, to keep the correct libtool macros in-tree.

although my package already has a macro dir != m4.

How to reproduce:

1) In an empty directory, save these two files:
============================ configure.ac ============================
AC_INIT([dummy], [0])
AC_CONFIG_AUX_DIR([build-aux])
AM_INIT_AUTOMAKE
AC_CONFIG_HEADERS([config.h])
AC_CONFIG_FILES([Makefile glm4/Makefile])
AC_OUTPUT
======================================================================
============================ Makefile.am =============================
AUTOMAKE_OPTIONS = 1.5 foreign
SUBDIRS = glm4
ACLOCAL_AMFLAGS = -I glm4
======================================================================

2)
$ libtoolize --copy
libtoolize: putting auxiliary files in AC_CONFIG_AUX_DIR, `build-aux'.
libtoolize: copying file `build-aux/ltmain.sh'
libtoolize: putting macros in `glm4'.
libtoolize: copying file `glm4/libtool.m4'
libtoolize: copying file `glm4/ltoptions.m4'
libtoolize: copying file `glm4/ltsugar.m4'
libtoolize: copying file `glm4/ltversion.m4'
libtoolize: copying file `glm4/lt~obsolete.m4'
libtoolize: Remember to add `LT_INIT' to configure.ac.
libtoolize: Consider adding `AC_CONFIG_MACRO_DIR([m4])' to configure.ac and
libtoolize: rerunning libtoolize, to keep the correct libtool macros in-tree.

It _has_ noticed that the autoconf macros belong in directory glm4/.
Then

  * Why is it telling me to put _another_ macro dir into configure.ac?
    In other words, why does it not recommend to add
      AC_CONFIG_MACRO_DIR([glm4])
    ?

  * Why is it telling me to use AC_CONFIG_MACRO_DIR at all? Since it
    has already determined that 'glm4' is my local macro dir (presumably
    by analyzing the ACLOCAL_AMFLAGS in Makefile.am), what would be the
    point of declaring it a second time, through AC_CONFIG_MACRO_DIR ?

Bruno