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

diff --git a/coreutils/echo.c b/coreutils/echo.c
index 851d2ef..860853f 100644
--- a/coreutils/echo.c
+++ b/coreutils/echo.c
@@ -119,8 +119,8 @@
 
 /* This is a NOFORK applet. Be very careful! */
 
-int echo_main(int argc, char** argv);
-int echo_main(int argc, char** argv)
+int echo_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
+int echo_main(int argc, char **argv)
 {
 	return bb_echo(argv);
 }