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/main.c

@@ -22,6 +22,7 @@
 #ifdef HAVE_CONFIG_H
 #include "config.h"
 #endif
+#include "openocd.h"
 
 /* This is the main entry for developer PC hosted OpenOCD.
  *
@@ -32,8 +33,6 @@
  * Those applications will have their own main() implementation
  * and use bits and pieces from openocd.c. */
 
-extern int openocd_main(int argc, char *argv[]);
-
 int main(int argc, char *argv[])
 {
 	return openocd_main(argc, argv);