include headers when we try to to find the symbols, since it might not be a variable...

cf/check-var.m4

@@ -9,7 +9,8 @@ m4_ifval([$2],[
 	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([[extern int $1;
+AC_LINK_IFELSE([AC_LANG_PROGRAM([[$2
+extern int $1;
 int foo(void) { return $1; }]],[[foo()]])],
 	    [ac_cv_var_$1=yes],[ac_cv_var_$1=no])
 fi