add openocd.h for top-level declarations

Create src/openocd.h to hold declarations previously made internally
by src/main.c and src/server/server.c.  This ensures all functions
are verified to be in-sync at compile time (rather than at link),
making it easier to track down bugs.

src/server/server.c

@@ -29,6 +29,7 @@
 
 #include "server.h"
 #include "target.h"
+#include "openocd.h"
 
 #include <signal.h>
 
@@ -285,9 +286,6 @@ int remove_services(void)
 	return ERROR_OK;
 }
 
-extern void openocd_sleep_prelude(void);
-extern void openocd_sleep_postlude(void);
-
 int server_loop(struct command_context *command_context)
 {
 	struct service *service;