Move messages.c to libbb. Make each string in messages.c be its own .o file.

This way, we can new get rid of all that tedious #define rubbish we used to
need to enable specific messages.  This way is enormously simpler, and as a
bonus also ends up saving us 96 bytes.
 -Erik

archival/gunzip.c

@@ -65,10 +65,6 @@ static char *license_msg[] = {
 #include <unistd.h>
 #include <getopt.h>
 #include "busybox.h"
-#define BB_DECLARE_EXTERN
-#define bb_need_memory_exhausted
-#define bb_need_name_too_long
-#include "messages.c"
 
 extern int gunzip_main(int argc, char **argv)
 {