Move some gcc extensions to new gcc_extensions.h header

- Move ATTRIBUTE_PRINTF/ATTRIBUTE_SCANF from _ansi.h
  They are not related at all to this file, and this broke compilation
  with Code Sourcery GCC which ships its own _ansi.h
- Move LIKELY/UNLIKELY from system.h

There is likely a lot more GCC extensions used everywhere in the source,
conditionally on __GNUC__ or unconditionally

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@27548 a1c6a512-1295-4272-9138-f99709370657

firmware/include/gcc_extensions.h

@@ -0,0 +1,46 @@
+/***************************************************************************
+ *             __________               __   ___.
+ *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
+ *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
+ *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
+ *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
+ *                     \/            \/     \/    \/            \/
+ *
+ * Copyright © 2010 Rafaël Carré
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ ****************************************************************************/
+
+#ifndef _GCC_EXTENSIONS_H_
+#define _GCC_EXTENSIONS_H_
+
+/* Support for some GCC extensions */
+
+/* Compile time check of format for printf/scanf like functions */
+#ifdef __GNUC__
+#define ATTRIBUTE_PRINTF(fmt, arg1) __attribute__( ( format( printf, fmt, arg1 ) ) )
+#define ATTRIBUTE_SCANF(fmt, arg1) __attribute__( ( format( scanf, fmt, arg1 ) ) )
+#else
+#define ATTRIBUTE_PRINTF(fmt, arg1)
+#define ATTRIBUTE_SCANF(fmt, arg1)
+#endif
+
+
+/* Use to give gcc hints on which branch is most likely taken */
+#if defined(__GNUC__) && __GNUC__ >= 3
+#define LIKELY(x)   __builtin_expect(!!(x), 1)
+#define UNLIKELY(x) __builtin_expect(!!(x), 0)
+#else
+#define LIKELY(x)   (x)
+#define UNLIKELY(x) (x)
+#endif
+
+
+#endif /* _GCC_EXTENSIONS_H_ */