Adding silc-client as irssi plugin

Alone, with its own irssi, doesn't build.

pkgs/applications/networking/instant-messengers/silc-client/server_setup.patch

@@ -0,0 +1,28 @@
+Add function to replace the behaviour of server_setup_find_port which was removed from irssi on revision 5125. Fixes bug #577501.
+--- a/apps/irssi/src/silc/core/client_ops.c
++++ b/apps/irssi/src/silc/core/client_ops.c
+@@ -2790,6 +2790,15 @@
+   silc_free(a);
+ }
+ 
++/* helper function to emulate server_setup_find_port */
++static SERVER_SETUP_REC *silc_server_setup_find_port(const char *address,
++						     int port) {
++  SERVER_SETUP_REC *rec;
++
++  rec = server_setup_find(address, port, NULL);
++  return (rec == NULL || rec->port != port) ? NULL : rec;
++}
++
+ /* Find authentication data by hostname and port. The hostname may be IP
+    address as well.*/
+ 
+@@ -2811,7 +2820,7 @@
+ 
+   /* Check whether we find the password for this server in our
+      configuration.  If it's set, always send it server. */
+-  setup = server_setup_find_port(hostname, port);
++  setup = silc_server_setup_find_port(hostname, port);
+   if (setup && setup->password) {
+     completion(SILC_AUTH_PASSWORD, setup->password, strlen(setup->password),
+ 	       context);

pkgs/top-level/all-packages.nix

@@ -1568,6 +1568,10 @@ let
 
   siege = callPackage ../tools/networking/siege {};
 
+  silc_client = callPackage ../applications/networking/instant-messengers/silc-client { };
+
+  silc_server = callPackage ../servers/silc-server { };
+
   sleuthkit = callPackage ../tools/system/sleuthkit {};
 
   slimrat = callPackage ../tools/networking/slimrat {
@@ -6221,8 +6225,6 @@ let
 
   shadow = callPackage ../os-specific/linux/shadow { };
 
-  silc_server = callPackage ../servers/silc-server { };
-
   splashutils = callPackage ../os-specific/linux/splashutils/default.nix { };
 
   statifier = builderDefsPackage (import ../os-specific/linux/statifier) { };