Work around bugs in pre-3.0 UWIN ksh makes bash-2.02.2 panic

[Daniel Goujot]

maremma:/4go/tmp/make-3.80% sh --version
GNU bash, version 2.01.1(1)-release (i586-pc-linux-gnu)
Copyright 1997 Free Software Foundation, Inc.

This shell will make segmentation fault on these lines :

# Work around bugs in pre-3.0 UWIN ksh.
$as_unset ENV MAIL MAILPATH
PS1='$ '
PS2='> '
PS4='+ '

(found in make-3.80/configure, make-3.80/config.status, and maybe other
places)
In installation of gmake-3.80, ./configure step won't work unless these
lines are removed.

        Daniel Goujot