lemon-graph: fix C++17 build

pkgs/development/libraries/lemon-graph/default.nix

···
   # error: no viable conversion from ...
   doCheck = !stdenv.isDarwin;
 
+  patches = [
+    # error: ISO C++17 does not allow 'register' storage class specifier
+    ./remove-register.patch
+  ];
+
   meta = with lib; {
     homepage = "https://lemon.cs.elte.hu/trac/lemon";
     description = "Efficient library for combinatorial optimization tasks on graphs and networks";

pkgs/development/libraries/lemon-graph/remove-register.patch

···
+diff --git a/lemon/random.h b/lemon/random.h
+index 8de74ede8a..f9861f3916 100644
+--- a/lemon/random.h
++++ b/lemon/random.h
+@@ -249,8 +249,8 @@ namespace lemon {
+ 
+         current = state + length;
+ 
+-        register Word *curr = state + length - 1;
+-        register long num;
++        Word *curr = state + length - 1;
++        long num;
+ 
+         num = length - shift;
+         while (num--) {