HAVM_PROG macro does not work with Autoconf 2.72+

Issue highlighted by @MajoraSans.

You need Autoconf 2.72+ to reproduce this issue.

root@c26b2669a83f:/opt/tiger/havm-master# autoconf --version
autoconf (GNU Autoconf) 2.72
Copyright (C) 2023 Free Software Foundation, Inc.
License GPLv3+/Autoconf: GNU GPL version 3 or later
<https://gnu.org/licenses/gpl.html>, <https://gnu.org/licenses/exceptions.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Written by David J. MacKenzie and Akim Demaille.
root@c26b2669a83f:/opt/tiger/havm-master# ./bootstrap 
autoreconf: export WARNINGS=
autoreconf: Entering directory '.'
autoreconf: configure.ac: not using Gettext
autoreconf: running: aclocal --force -I build-aux
autoreconf: configure.ac: tracing
autoreconf: configure.ac: not using Libtool
autoreconf: configure.ac: not using Intltool
autoreconf: configure.ac: not using Gtkdoc
autoreconf: running: /usr/bin/autoconf --force
autoreconf: configure.ac: not using Autoheader
autoreconf: running: automake --add-missing --copy --force-missing
autoreconf: Leaving directory '.'
root@c26b2669a83f:/opt/tiger/havm-master# ./configure
checking for a BSD-compatible install... /usr/bin/install -c
checking whether build environment is sane... yes
checking for a race-free mkdir -p... /usr/bin/mkdir -p
checking for gawk... gawk
checking whether make sets $(MAKE)... yes
checking whether make supports nested variables... yes
checking for ghc... ghc
./configure: line 2632: syntax error near unexpected token `;;'
./configure: line 2632: `esac ;;'
root@c26b2669a83f:/opt/tiger/havm-master#