add -fvisibility=hidden to CC flags, mark XXX_main functions

EXTERNALLY_VISIBLE. 5% size reduction of libbusybox.so

coreutils/uniq.c

@@ -27,7 +27,7 @@ static FILE *xgetoptfile_uniq_s(char **argv, int read0write2)
 	return (read0write2) ? stdout : stdin;
 }
 
-int uniq_main(int argc, char **argv);
+int uniq_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int uniq_main(int argc, char **argv)
 {
 	FILE *in, *out;