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

diff --git a/util-linux/fbset.c b/util-linux/fbset.c
index a2b8b38..f67a283 100644
--- a/util-linux/fbset.c
+++ b/util-linux/fbset.c
@@ -309,7 +309,7 @@
 #ifdef STANDALONE
 int main(int argc, char **argv)
 #else
-int fbset_main(int argc, char **argv);
+int fbset_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int fbset_main(int argc, char **argv)
 #endif
 {