undef HAVE_BUILTIN___BUILTIN_CHOOSE_EXPR_CONSTANT_P on GCC 4.8

GCC 4.8 with optimization causes error if it compiles following code.
[Bug #14221]

```c
__builtin_choose_expr(__builtin_constant_p(b),0,1)
```

https://github.com/ruby/ruby/pull/1778

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@61429 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

include/ruby/defines.h

@@ -72,6 +72,17 @@ extern "C" {
 #  define GCC_VERSION_SINCE(major, minor, patchlevel) 0
 # endif
 #endif
+#ifndef GCC_VERSION_BEFORE
+# if defined(__GNUC__) && !defined(__INTEL_COMPILER) && !defined(__clang__)
+#  define GCC_VERSION_BEFORE(major, minor, patchlevel) \
+    ((__GNUC__ < (major)) ||  \
+     ((__GNUC__ == (major) && \
+       ((__GNUC_MINOR__ < (minor)) || \
+        (__GNUC_MINOR__ == (minor) && __GNUC_PATCHLEVEL__ <= (patchlevel))))))
+# else
+#  define GCC_VERSION_BEFORE(major, minor, patchlevel) 0
+# endif
+#endif
 
 /* likely */
 #if __GNUC__ >= 3

include/ruby/ruby.h

@@ -26,15 +26,17 @@ extern "C" {
 #include RUBY_EXTCONF_H
 #endif
 
+#include "defines.h"
+
 #if defined(__cplusplus)
 /* __builtin_choose_expr and __builtin_types_compatible aren't available
  * on C++.  See https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html */
 # undef HAVE_BUILTIN___BUILTIN_CHOOSE_EXPR_CONSTANT_P
 # undef HAVE_BUILTIN___BUILTIN_TYPES_COMPATIBLE_P
+#elif GCC_VERSION_BEFORE(4,8,6) /* Bug #14221 */
+# undef HAVE_BUILTIN___BUILTIN_CHOOSE_EXPR_CONSTANT_P
 #endif
 
-#include "defines.h"
-
 #ifndef ASSUME
 # ifdef UNREACHABLE
 #   define ASSUME(x) (RB_LIKELY(!!(x)) ? (void)0 : UNREACHABLE)