* Experimental feature: allow a derivation to tell the build hook that

it requires a certain feature on the build machine, e.g.

    requiredSystemFeatures = [ "kvm" ];

  We need this in Hydra to make sure that builds that require KVM
  support are forwarded to machines that have KVM support.  Probably
  this should also be enforced for local builds.

src/libutil/util.hh

@@ -280,6 +280,11 @@ MakeError(Interrupted, BaseError)
 Strings tokenizeString(const string & s, const string & separators = " \t\n\r");
 
 
+/* Concatenate the given strings with a separator between the
+   elements. */
+string concatStringsSep(const string & sep, const Strings & ss);
+
+
 /* Convert the exit status of a child as returned by wait() into an
    error string. */
 string statusToString(int status);