Automake generates rules to automatically rebuild Makefiles,
configure, and other derived files like Makefile.in.
If you are using AM_MAINTAINER_MODE in configure.in, then
these automatic rebuilding rules are only enabled in maintainer mode.
Sometimes you need to run aclocal with an argument like -I
to tell it where to find .m4 files. Since sometimes make
will automatically run aclocal, you need a way to specify these
arguments. You can do this by defining ACLOCAL_AMFLAGS; this
holds arguments which are passed verbatim to aclocal. This variable
is only useful in the top-level Makefile.am.