autoconf picks up all its macro
definitions from /usr/share/autoconf on a system where autoconf is
installed in /usr/bin. I found that AC_MSG_ERROR is re-directed in
autoconf/general.m4 to AS_ERROR:
m4_copy([AS_ERROR], [AC_MSG_ERROR])
Then AS_ERROR is defined in m4sugar/m4sh.m4 as:
# AS_ERROR(ERROR, [EXIT-STATUS = 1])
# ----------------------------------
m4_define([AS_ERROR],
[{ AS_MESSAGE([error: $1], [2])
AS_EXIT([$2]); }[]dnl
])# AS_ERROR
You will probably find these two definitions on your system.
IIRC, I had the same problem as you on a PPC Mac and assumed that
separate installations of the tool probably interfered with each
other.