[Bugfix] Compile VeNCrypt extension only when gnutls is enabled and available.


git-svn-id: svn://svn.code.sf.net/p/tigervnc/code/trunk@4049 3789f03b-4d11-0410-bbf8-ca57d06f2519
diff --git a/common/rfb/SSecurityTLSBase.cxx b/common/rfb/SSecurityTLSBase.cxx
index 2fec9bc..6801210 100644
--- a/common/rfb/SSecurityTLSBase.cxx
+++ b/common/rfb/SSecurityTLSBase.cxx
@@ -23,7 +23,9 @@
 #include <config.h>
 #endif
 
-#ifdef HAVE_GNUTLS
+#ifndef HAVE_GNUTLS
+#error "This source should not be compiled without HAVE_GNUTLS defined"
+#endif
 
 #include <rfb/SSecurityTLSBase.h>
 #include <rfb/SConnection.h>
@@ -143,4 +145,3 @@
   return true;
 }
 
-#endif /* HAVE_GNUTLS */