xxdiff-tip: Build with qt59

pkgs/development/tools/misc/xxdiff/tip.nix

···
 
   buildInputs = [ qtbase ];
 
+  # Fixes build with Qt 5.9
+  NIX_CFLAGS_COMPILE = [ "-std=c++11" ];
+
   preConfigure = ''
     cd src
     make -f Makefile.bootstrap

pkgs/top-level/all-packages.nix

···
   xxdiff = callPackage ../development/tools/misc/xxdiff {
     bison = bison2;
   };
-  xxdiff-tip = qt56.callPackage ../development/tools/misc/xxdiff/tip.nix { };
+  xxdiff-tip = libsForQt5.callPackage ../development/tools/misc/xxdiff/tip.nix { };
 
   yacc = bison;