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

EXTERNALLY_VISIBLE. 5% size reduction of libbusybox.so

debianutils/mktemp.c

@@ -11,7 +11,7 @@
 
 #include "libbb.h"
 
-int mktemp_main(int argc, char **argv);
+int mktemp_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int mktemp_main(int argc, char **argv)
 {
 	unsigned long flags = getopt32(argv, "dqt");

debianutils/pipe_progress.c

@@ -14,7 +14,7 @@
 /* Read a block of data from stdin, write it to stdout.
  * Activity is indicated by a '.' to stderr
  */
-int pipe_progress_main(int argc, char **argv);
+int pipe_progress_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int pipe_progress_main(int argc, char **argv)
 {
 	RESERVE_CONFIG_BUFFER(buf, PIPE_PROGRESS_SIZE);

debianutils/run_parts.c

@@ -110,7 +110,7 @@ static const char runparts_longopts[] ALIGN1 =
 	;
 #endif
 
-int run_parts_main(int argc, char **argv);
+int run_parts_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int run_parts_main(int argc, char **argv)
 {
 	const char *umask_p = "22";

debianutils/start_stop_daemon.c

@@ -234,7 +234,7 @@ enum {
 	OPT_NICELEVEL  = 0x4000 * ENABLE_FEATURE_START_STOP_DAEMON_FANCY, // -N
 };
 
-int start_stop_daemon_main(int argc, char **argv);
+int start_stop_daemon_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int start_stop_daemon_main(int argc, char **argv)
 {
 	unsigned opt;

debianutils/which.c

@@ -12,7 +12,7 @@
 
 #include "libbb.h"
 
-int which_main(int argc, char **argv);
+int which_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int which_main(int argc, char **argv)
 {
 	int status = EXIT_SUCCESS;