libbb: introduce kernel-style BUILD_BUG_ON()

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

networking/tftp.c

@@ -129,10 +129,9 @@ struct globals {
 #endif
 } FIX_ALIASING;
 #define G (*(struct globals*)&bb_common_bufsiz1)
-struct BUG_G_too_big {
-	char BUG_G_too_big[sizeof(G) <= COMMON_BUFSIZE ? 1 : -1];
-};
-#define INIT_G() do { } while (0)
+#define INIT_G() do { \
+	BUILD_BUG_ON(sizeof(G) > COMMON_BUFSIZE); \
+} while (0)
 
 #define G_error_pkt_reason (G.error_pkt[3])
 #define G_error_pkt_str    ((char*)(G.error_pkt + 4))