Proper way to tell aclocal about ./m4?

[Kevin P. Fleming]

I have created an m4 directory in my source tree, and put some macros 
downloaded from the autoconf macro archive in there. I also added

AC_CONFIG_MACRO_DIR([m4])

to configure.ac, and this causes autoreconf to (correctly) put 
libtool.m4 and ltdl.m4 into the m4 directory.

However, aclocal does not pick up the contents of this directory into 
aclocal.m4 unless I add

ACLOCAL_FLAGS=-I m4

to Makefile.am. Is this the proper way to get aclocal to pick up these 
macros?