bug in autoconf 2.59 under Interix 3.5

[Bob Frazier]

some time ago I downloaded a tarball for autoconf 2.59 so I hope this has
already been addressed.  if not...

Running the newest Interix 3.5, following build of gnu 'make' and grep
(necessary for various things), I build m4 1.4.1 successfully and then
attempted to build autoconf 2.59 .  The build succeeded until the script
tests/autom4te, line 18 had problem (mismatched 'if')

The line in autom4te read as follows:
if ((MAIL=60\; unset MAIL) || exit) ; then

I changed it to this

if ($(MAIL=60\; unset MAIL) || exit) ; then

then it ran fine with Interix.

Interix is using ksh, KSH_VERSION evaluates to the following string:
@(#)PD KSH v5.2.13 97/10/27 [Interix: 2003/11/07][i18n]