AC_DEFUN(AM_PATH_LIBMCRYPT,
should be replaced with
AC_DEFUN([AM_PATH_LIBMCRYPT],
in lib/libmcrypt.m4, else with automake-1.9 I receive this message:
/usr/share/aclocal/libmcrypt.m4:17: warning: underquoted definition of AM_PATH_LIBMCRYPT
run info '(automake)Extending aclocal'
or see http://sources.redhat.com/automake/automake.html#Extending-aclocal