Upstream re-ran autoconf here, eliminating these problematic parts:

commit dfbd6bd6c6341e55cea7c4f89b9589eccc94459c
Author: Stefan Vigerske <svigerske@gams.com>
Date:   Thu May 6 12:46:51 2021 +0200

    update to current autotools

diff --git a/configure b/configure
index f1d1c8e77a07d248..533f70fcf22511ef 100755
--- a/configure
+++ b/configure
@@ -2514,7 +2514,7 @@ if { (eval echo "$as_me:$LINENO: \"$ac_compile\"") >&5
   echo "$as_me:$LINENO: \$? = $ac_status" >&5
   (exit $ac_status); }; }; then
   for ac_declaration in \
-   '' \
+   '#include <stdlib.h>' \
    'extern "C" void std::exit (int) throw (); using std::exit;' \
    'extern "C" void std::exit (int); using std::exit;' \
    'extern "C" void exit (int) throw ();' \
@@ -3314,7 +3314,7 @@ else
   fi
 fi
 for ac_declaration in \
-   '' \
+   '#include <stdlib.h>' \
    'extern "C" void std::exit (int) throw (); using std::exit;' \
    'extern "C" void std::exit (int); using std::exit;' \
    'extern "C" void exit (int) throw ();' \
@@ -6906,8 +6906,8 @@ main ()
   for (i = 0; i < 256; i++)
     if (XOR (islower (i), ISLOWER (i))
 	|| toupper (i) != TOUPPER (i))
-      exit(2);
-  exit (0);
+      return 2;
+  return 0;
 }
 _ACEOF
 rm -f conftest$ac_exeext