charon-svc: Implement a Windows IKE service using libcharon

The resulting binary can be either run as Windows service or directly as
console application.

src/Makefile.am

@@ -116,6 +116,10 @@ if USE_CMD
   SUBDIRS += charon-cmd
 endif
 
+if USE_SVC
+  SUBDIRS += charon-svc
+endif
+
 if USE_LIBPTTLS
   SUBDIRS += pt-tls-client
 endif