add -fvisibility=hidden to CC flags, mark XXX_main functions
EXTERNALLY_VISIBLE. 5% size reduction of libbusybox.so

diff --git a/coreutils/od_bloaty.c b/coreutils/od_bloaty.c
index 1bd1b0c..9655c23 100644
--- a/coreutils/od_bloaty.c
+++ b/coreutils/od_bloaty.c
@@ -1196,7 +1196,7 @@
 	check_and_close();
 }
 
-int od_main(int argc, char **argv);
+int od_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int od_main(int argc, char **argv)
 {
 	static const struct suffix_mult bkm[] = {