configure.in: get rid of clang fatal error

* configure.in (ac_cv_func___builtin_setjmp): get rid of a bug in
  clang 3.3 and 3.4, which __builtin_setjmp() causes fatal error
  in backend, linker error, or segmentation fault.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45515 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

configure.in

@@ -2080,15 +2080,16 @@ fi
 AC_CACHE_CHECK(for __builtin_setjmp, ac_cv_func___builtin_setjmp,
     [
     ac_cv_func___builtin_setjmp=no
-    for cast in "" "(void *)"; do
+    for cast in "" "(void **)"; do
 	RUBY_WERROR_FLAG(
 	[AC_TRY_LINK([@%:@include <setjmp.h>
 	    @%:@include <stdio.h>
 	    jmp_buf jb;
-	    void t(void) {__builtin_longjmp($cast jb, 1);}],
+	    void t(void) {__builtin_longjmp($cast jb, 1);}
+	    int jump(void) {(void)(__builtin_setjmp($cast jb) ? 1 : 0); return 0;}],
 	    [
 	    void (*volatile f)(void) = t;
-	    if (!__builtin_setjmp($cast jb)) printf("%d\n", f != 0);
+	    if (!jump()) printf("%d\n", f != 0);
 	    ],
 	    [ac_cv_func___builtin_setjmp="yes with cast ($cast)"])
 	])