add #include guard hack

According to MSVC manual (*1), cl.exe can skip including a header file
when that:

- contains #pragma once, or
- starts with #ifndef, or
- starts with #if ! defined.

GCC has a similar trick (*2), but it acts more stricter (e. g. there
must be _no tokens_ outside of #ifndef...#endif).

Sun C lacked #pragma once for a looong time.  Oracle Developer Studio
12.5 finally implemented it, but we cannot assume such recent version.

This changeset modifies header files so that each of them include
strictly one #ifndef...#endif.  I believe this is the most portable way
to trigger compiler optimizations. [Bug #16770]

*1: https://docs.microsoft.com/en-us/cpp/preprocessor/once
*2: https://gcc.gnu.org/onlinedocs/cppinternals/Guard-Macros.html

1 files changed, 11 insertions, 13 deletions

diff --git a/internal.h b/internal.h
index 3c65164f3d..c39fa18174 100644
--- a/internal.h
+++ b/internal.h
@@ -1,17 +1,15 @@
-/**********************************************************************
-
-  internal.h -
-
-  $Author$
-  created at: Tue May 17 11:42:20 JST 2011
-
-  Copyright (C) 2011 Yukihiro Matsumoto
-
-**********************************************************************/
-
-#ifndef RUBY_INTERNAL_H
+#ifndef RUBY_INTERNAL_H                                  /*-*-C-*-vi:se ft=c:*/
 #define RUBY_INTERNAL_H 1
-
+/**
+ * @file
+ * @author     $Author$
+ * @date       Tue May 17 11:42:20 JST 2011
+ * @copyright  Copyright (C) 2011 Yukihiro Matsumoto
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ */
 #include "ruby/3/config.h"
 
 #ifdef __cplusplus