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-network.c

@@ -0,0 +1,144 @@
+/*
+ * Stub version of the whole networking abstraction.
+ */
+
+#include "putty.h"
+#include "network.h"
+
+struct SockAddr {
+    int dummy;
+};
+
+void sk_init(void)
+{
+}
+
+void sk_cleanup(void)
+{
+}
+
+SockAddr *sk_namelookup(const char *host, char **canonicalname,
+                        int address_family)
+{
+    return snew(SockAddr);
+}
+SockAddr *sk_nonamelookup(const char *host)
+{
+    return snew(SockAddr);
+}
+
+void sk_getaddr(SockAddr *addr, char *buf, int buflen)
+{
+    strncpy(buf, "nonsense", buflen);
+}
+
+bool sk_addr_needs_port(SockAddr *addr)
+{
+    return true;
+}
+
+bool sk_hostname_is_local(const char *name)
+{
+    return false;
+}
+
+bool sk_address_is_local(SockAddr *addr)
+{
+    return false;
+}
+
+bool sk_address_is_special_local(SockAddr *addr)
+{
+    return false;
+}
+
+int sk_addrtype(SockAddr *addr)
+{
+    return ADDRTYPE_UNSPEC;
+}
+
+void sk_addrcopy(SockAddr *addr, char *buf)
+{
+}
+
+void sk_addr_free(SockAddr *addr)
+{
+    sfree(addr);
+}
+
+SockAddr *sk_addr_dup(SockAddr *addr)
+{
+    return snew(SockAddr);
+}
+
+Socket *sk_new(SockAddr *addr, int port, bool privport, bool oobinline,
+               bool nodelay, bool keepalive, Plug *plug)
+{
+    return new_error_socket_fmt(
+        plug, "no actual networking in this application");
+}
+
+Socket *sk_newlistener(const char *srcaddr, int port, Plug *plug,
+                       bool local_host_only, int orig_address_family)
+{
+    return new_error_socket_fmt(
+        plug, "no actual networking in this application");
+}
+
+void *(sk_getxdmdata)(Socket *sock, int *lenp)
+{
+    return NULL;
+}
+
+void plug_closing_errno(Plug *plug, int error)
+{
+    plug_closing(plug, PLUGCLOSE_ERROR, "dummy");
+}
+
+const char *sk_addr_error(SockAddr *addr)
+{
+    return "no actual network addresses in this application";
+}
+
+int net_service_lookup(const char *service)
+{
+    return 0;
+}
+
+char *get_hostname(void)
+{
+    return dupstr("dummy-hostname");
+}
+
+SockAddr *platform_get_x11_unix_address(const char *sockpath, int displaynum)
+{
+    return snew(SockAddr);
+}
+
+SockAddr *unix_sock_addr(const char *path)
+{
+    return snew(SockAddr);
+}
+
+SockAddr *sk_namedpipe_addr(const char *pipename)
+{
+    return snew(SockAddr);
+}
+
+Socket *new_unix_listener(SockAddr *listenaddr, Plug *plug)
+{
+    return new_error_socket_fmt(
+        plug, "no actual networking in this application");
+}
+
+Socket *platform_start_subprocess(const char *cmd, Plug *plug,
+                                  const char *prefix)
+{
+    return new_error_socket_fmt(
+        plug, "no actual networking in this application");
+}
+
+#ifdef PUTTY_WINDOWS_PLATFORM_H
+void plug_closing_system_error(Plug *plug, DWORD error) {}
+void plug_closing_winsock_error(Plug *plug, DWORD error) {}
+#endif