MINOR: global: export the display_version() symbol

Export the display_version() function which can be used elsewhere than
in haproxy.c

include/haproxy/global.h

@@ -62,6 +62,7 @@ int delete_oldpid(int pid);
 void hap_register_build_opts(const char *str, int must_free);
 int split_version(const char *version, unsigned int *value);
 int compare_current_version(const char *version);
+void display_version();
 
 void mworker_accept_wrapper(int fd);
 void mworker_reload(void);

src/haproxy.c

@@ -490,7 +490,7 @@ int compare_current_version(const char *version)
 	return 0;
 }
 
-static void display_version()
+void display_version()
 {
 	struct utsname utsname;