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

diff --git a/init/init.c b/init/init.c
index 5e84011..409e8c4 100644
--- a/init/init.c
+++ b/init/init.c
@@ -882,7 +882,7 @@
 }
 #endif  /* FEATURE_USE_INITTAB */
 
-int init_main(int argc, char **argv);
+int init_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int init_main(int argc, char **argv)
 {
 	struct init_action *a;