add -fvisibility=hidden to CC flags, mark XXX_main functions

EXTERNALLY_VISIBLE. 5% size reduction of libbusybox.so

miscutils/eject.c

@@ -25,7 +25,7 @@
 #define FLAG_CLOSE  1
 #define FLAG_SMART  2
 
-int eject_main(int argc, char **argv);
+int eject_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int eject_main(int argc, char **argv)
 {
 	unsigned long flags;