Add lots more stub versions of standard code modules.

These are all going to be used by a test program I have in the works,
which will need to link against a lot more of the code base than any
so far. So we need a pile of new stubs.

The trickiest of these was stubs/no-network.c, which had to
conditionally define a couple of extra network functions, because
there are Windows-specific plug_closing_system_error and
plug_closing_winsock_error functions.

stubs/no-timing.c

@@ -19,3 +19,8 @@ unsigned long schedule_timer(int ticks, timer_fn_t fn, void *ctx)
 void expire_timer_context(void *ctx)
 {
 }
+
+unsigned long timing_last_clock(void)
+{
+    return 0;
+}