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

diff --git a/editors/vi.c b/editors/vi.c
index 25c8234..249bf29 100644
--- a/editors/vi.c
+++ b/editors/vi.c
@@ -311,7 +311,7 @@
 	fputs(out, stdout);
 }
 
-int vi_main(int argc, char **argv);
+int vi_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int vi_main(int argc, char **argv)
 {
 	int c;