[PATCH] Use more gcc extensions in the Linux headers

__builtin_types_compatible_p() has been around since gcc 2.95, and we
don't use it anywhere.  This patch quietly fixes that.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff -r f0ff8138f993 include/linux/kernel.h
--- a/include/linux/kernel.h	Fri Mar 09 16:40:25 2007 +1100
+++ b/include/linux/kernel.h	Fri Mar 09 16:44:04 2007 +1100
@@ -35,7 +35,9 @@ extern const char linux_proc_banner[];
 #define ALIGN(x,a)		__ALIGN_MASK(x,(typeof(x))(a)-1)
 #define __ALIGN_MASK(x,mask)	(((x)+(mask))&~(mask))
 
-#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
+#define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0])			      \
+	+ sizeof(typeof(int[1 - 2*!!__builtin_types_compatible_p(typeof(arr), \
+		 typeof(&arr[0]))]))*0)
 #define FIELD_SIZEOF(t, f) (sizeof(((t*)0)->f))
 #define DIV_ROUND_UP(n,d) (((n) + (d) - 1) / (d))
 #define roundup(x, y) ((((x) + ((y) - 1)) / (y)) * (y))