See here for more info:
http://lists.gnu.org/archive/html/libtool-patches/2009-06/msg00028.html
We workaround by explicitly running _LT_PROG_ECHO_BACKSLASH before
LT_PATH_LD.
# aclocal doesn't resolve those automatically, so we need to call
# LT_PATH_LD and LTSUGAR_VERSION to pull in libtool.m4 and ltsugar.m4
# where the required dependencies are m4_defun'd.
+ AC_REQUIRE([_LT_PROG_ECHO_BACKSLASH])dnl
AC_REQUIRE([LT_PATH_LD])dnl
AC_REQUIRE([LTSUGAR_VERSION])dnl
AC_REQUIRE([AC_PROG_CC])dnl