[1/2] Make BUILD_BUG_ON fail at compile time.

["Andi Kleen" <ak@suse.de>]

Make BUILD_BUG_ON fail at compile time.

Force a compiler error instead of a link error, because they
are easier to track down. Idea stolen from code by Jan Beulich.

Cc: jbeulich@novell.com

Index: linux/include/linux/kernel.h
===================================================================
--- linux.orig/include/linux/kernel.h
+++ linux/include/linux/kernel.h
@@ -307,8 +307,8 @@ struct sysinfo {
 	char _f[20-2*sizeof(long)-sizeof(int)];	/* Padding: libc5 uses this.. */
 };
 
-extern void BUILD_BUG(void);
-#define BUILD_BUG_ON(condition) do { if (condition) BUILD_BUG(); } while(0)
+/* Force a compilation error if condition is false */
+#define BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)]))
 
 #ifdef CONFIG_SYSCTL
 extern int randomize_va_space;