dgsh: fix build with glibc 2.26

pkgs/shells/dgsh/default.nix

@@ -15,6 +15,8 @@ stdenv.mkDerivation rec {
     fetchSubmodules = true;
   };
 
+  patches = [ ./glibc-2.26.patch ];
+
   nativeBuildInputs = [ autoconf automake pkgconfig libtool check
     bison git gettext gperf perl texinfo help2man ncurses
   ];
@@ -31,6 +33,8 @@ stdenv.mkDerivation rec {
     make PREFIX=$out config
   '';
 
+  enableParallelBuilding = true;
+
   meta = with stdenv.lib; {
     description = "The Directed Graph Shell";
     homepage = http://www.dmst.aueb.gr/dds/sw/dgsh;