use _Static_assert with clang

* gc.c (__has_feature): move into internal.h.

* internal.h (__has_feature): ditto.

* internal.h (__has_extension): new macro.

* internal.h (STATIC_ASSERT): use _Static_assert with
  clang. [ruby-core:69931] [Bug ruby#11343]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@51242 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

Author: znz

ChangeLog

@@ -1,3 +1,14 @@
+Wed Jul 15 00:03:36 2015  Kazuhiro NISHIYAMA  <zn@mbf.nifty.com>
+
+	* gc.c (__has_feature): move into internal.h.
+
+	* internal.h (__has_feature): ditto.
+
+	* internal.h (__has_extension): new macro.
+
+	* internal.h (STATIC_ASSERT): use _Static_assert with
+	  clang. [ruby-core:69931] [Bug #11343]
+
 Wed Jul 15 00:00:00 2015  Kazuhiro NISHIYAMA  <zn@mbf.nifty.com>
 
 	* random.c (fill_random_bytes_syscall): fix compile error with

gc.c

@@ -35,10 +35,6 @@
 
 #undef rb_data_object_wrap
 
-#ifndef __has_feature
-# define __has_feature(x) 0
-#endif
-
 #ifndef HAVE_MALLOC_USABLE_SIZE
 # ifdef _WIN32
 #   define HAVE_MALLOC_USABLE_SIZE

internal.h

@@ -73,7 +73,15 @@ extern "C" {
     (__GNUC__ == (major) && __GNUC_MINOR__ > (minor)) || \
     (__GNUC__ == (major) && __GNUC_MINOR__ == (minor) && __GNUC_PATCHLEVEL__ >= (patchlevel))))
 
-#if GCC_VERSION_SINCE(4, 6, 0)
+#ifndef __has_feature
+# define __has_feature(x) 0
+#endif
+
+#ifndef __has_extension
+# define __has_extension __has_feature
+#endif
+
+#if GCC_VERSION_SINCE(4, 6, 0) || __has_extension(c_static_assert)
 # define STATIC_ASSERT(name, expr) _Static_assert(expr, #name ": " #expr)
 #else
 # define STATIC_ASSERT(name, expr) typedef int static_assert_##name##_check[1 - 2*!(expr)]