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

apps/codecs.h

@@ -31,7 +31,6 @@
 #define MEM 2
 #endif
 
-#include <_ansi.h>
 #include <stdbool.h>
 #include <stdlib.h>
 #include "strlcpy.h"
@@ -51,6 +50,8 @@
 #endif
 #include "settings.h"
 
+#include "gcc_extensions.h"
+
 #ifdef CODEC
 #if defined(DEBUG) || defined(SIMULATOR)
 #undef DEBUGF

apps/gui/splash.h

@@ -21,8 +21,9 @@
 
 #ifndef _GUI_SPLASH_H_
 #define _GUI_SPLASH_H_
-#include <_ansi.h>
+
 #include "screen_access.h"
+#include "gcc_extensions.h"
 
 /*
  * Puts a splash message centered on all the screens for a given period

apps/plugin.h

@@ -39,6 +39,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include "string-extra.h"
+#include "gcc_extensions.h"
 
 char* strncpy(char *, const char *, size_t);
 void* plugin_get_buffer(size_t *buffer_size);