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

diff --git a/archival/tar.c b/archival/tar.c
index 18b6267..3fe1886 100644
--- a/archival/tar.c
+++ b/archival/tar.c
@@ -769,7 +769,7 @@
 	;
 #endif
 
-int tar_main(int argc, char **argv);
+int tar_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int tar_main(int argc, char **argv)
 {
 	char (*get_header_ptr)(archive_handle_t *) = get_header_tar;