bug.h: sync BUILD_BUG stuff with Linux 4.13

As commit 84b8bf6d5d2a ("bug.h: move BUILD_BUG_* defines to
include/linux/bug.h") noted, include/linux/bug.h was locally
modified for U-Boot because the name conflict of error() caused
build errors at that time.

Now error() is gone, so we can fully sync BUILD_BUG* with Linux.
These macros are just compile-time utilities.  Nothing depends on
platform code, so it should make sense to simply copy Linux's ones.

Please note Linux split BUILD_BUG stuff out into <linux/build_bug.h>
by commit bc6245e5efd7.  Let's follow it.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 020ad16..0ea6c8f 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -476,7 +476,8 @@
 # define __compiletime_error_fallback(condition) do { } while (0)
 #endif
 
-#define __compiletime_assert(condition, msg, prefix, suffix)		\
+#ifdef __OPTIMIZE__
+# define __compiletime_assert(condition, msg, prefix, suffix)		\
 	do {								\
 		bool __cond = !(condition);				\
 		extern void prefix ## suffix(void) __compiletime_error(msg); \
@@ -484,6 +485,9 @@
 			prefix ## suffix();				\
 		__compiletime_error_fallback(__cond);			\
 	} while (0)
+#else
+# define __compiletime_assert(condition, msg, prefix, suffix) do { } while (0)
+#endif
 
 #define _compiletime_assert(condition, msg, prefix, suffix) \
 	__compiletime_assert(condition, msg, prefix, suffix)