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

EXTERNALLY_VISIBLE. 5% size reduction of libbusybox.so

selinux/matchpathcon.c

@@ -29,7 +29,7 @@ static int print_matchpathcon(char *path, int noprint)
 #define OPT_PREFIX      (1<<3)  /* -p */
 #define OPT_VERIFY      (1<<4)  /* -V */
 
-int matchpathcon_main(int argc, char **argv);
+int matchpathcon_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int matchpathcon_main(int argc, char **argv)
 {
 	int error = 0;