23.1 Autoconf Preliminaries
In a small package which only uses Autoconf, your own macros are placed
in the `aclocal.m4' file--this includes macros that you may have
obtained from third parties such as the Autoconf macro archive
(see section 23.5.1 Autoconf macro archive). If your package additionally uses
Automake, then these macros should be placed in `acinclude.m4'.
aclocal program from Automake reads in macro definitions from
`acinclude.m4' when generating `aclocal.m4'. When using
Automake, for instance, `aclocal.m4' will include the definitions
AM_ macros needed by Automake.
In larger projects, it's advisable to keep your custom macros in a more
organized structure. Autoconf version 2.15 will introduce a new
facility to explicitly include files from your `configure.in' file.
The details have not solidified yet, but it will almost certainly
include a mechanism for automatically included files with the correct
filename extension from a subdirectory, say `m4/'.