Merge staging into closure-size

The most complex problems were from dealing with switches reverted in
the meantime (gcc5, gmp6, ncurses6).
It's likely that darwin is (still) broken nontrivially.

pkgs/tools/graphics/graphviz/default.nix

@@ -31,6 +31,13 @@ stdenv.mkDerivation rec {
 
   configureFlags = stdenv.lib.optional (xorg == null) "--without-x";
 
+  postPatch = stdenv.lib.optionalString stdenv.isDarwin ''
+    for foo in cmd/dot/Makefile.in cmd/edgepaint/Makefile.in \
+                    cmd/mingle/Makefile.in plugin/gdiplus/Makefile.in; do
+      substituteInPlace "$foo" --replace "-lstdc++" "-lc++"
+    done
+  '';
+
   preBuild = ''
     sed -e 's@am__append_5 *=.*@am_append_5 =@' -i lib/gvc/Makefile
   '';