--- a/cf/check-var.m4	2013-04-24 20:07:35.000000000 -0600
+++ b/cf/check-var.m4	2020-01-07 11:36:36.493955390 -0700
@@ -6,12 +6,12 @@ AC_MSG_CHECKING(for $1)
 AC_CACHE_VAL(ac_cv_var_$1, [
 m4_ifval([$2],[
 	AC_LINK_IFELSE([AC_LANG_PROGRAM([[$2
-	void * foo(void) { return &$1; }]],[[foo()]])],
+	__attribute__ ((used)) void * foo(void) { return &$1; }]],[[foo()]])],
 	    [ac_cv_var_$1=yes],[ac_cv_var_$1=no])])
 if test "$ac_cv_var_$1" != yes ; then
 AC_LINK_IFELSE([AC_LANG_PROGRAM([[$2
 extern int $1;
-int foo(void) { return $1; }]],[[foo()]])],
+__attribute__ ((used)) int foo(void) { return $1; }]],[[foo()]])],
 	    [ac_cv_var_$1=yes],[ac_cv_var_$1=no])
 fi
 ])