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

diff --git a/coreutils/mkdir.c b/coreutils/mkdir.c
index d1a4380..6bdf76d 100644
--- a/coreutils/mkdir.c
+++ b/coreutils/mkdir.c
@@ -34,7 +34,7 @@
 	;
 #endif
 
-int mkdir_main(int argc, char **argv);
+int mkdir_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int mkdir_main(int argc, char **argv)
 {
 	mode_t mode = (mode_t)(-1);