If your autoconfiscated project uses local autoconf macros, then the initial bootstrapping will involve running `aclocal -I path/to/local/m4/macros'.
This is all fine and dandy, but during development the autotools might have to regenerate the aclocal.m4 file. When this happens, aclocal will be run without the -I flag, resulting in undefined macros errors. How to fix them?
The fix consists of adding the following substitution to your configure.ac:
AC_SUBST(ACLOCAL_AMFLAGS, "-I path/to/local/m4/macros")
This will ensure that we aclocal is automatically invoked by make, it will be called with the specified -I flag.