ALL: Massive 'const' cleanup

These changes facilitate more robust parameter type checking and helps
to identify unexpected coding errors.

Most simulators can now also be compiled with a C++ compiler without
warnings.

Additionally, these changes have also been configured to facilitate easier
backporting of simulator and device simulation modules to run under the
simh v3.9+ SCP framework.

sim_sock.h

@@ -46,6 +46,10 @@
 #ifndef SIM_SOCK_H_
 #define SIM_SOCK_H_    0
 
+#ifdef  __cplusplus
+extern "C" {
+#endif
+
 #if defined (_WIN32)                                    /* Windows */
 #include <winsock2.h>
 
@@ -126,4 +130,8 @@ int sim_getnames_sock (SOCKET sock, char **socknamebuf, char **peernamebuf);
 void sim_init_sock (void);
 void sim_cleanup_sock (void);
 
+#ifdef  __cplusplus
+}
+#endif
+
 #endif