all-packages: pass cxxStandard to or-tools

pkgs/development/libraries/abseil-cpp/default.nix

···
   cmakeFlags = [
     "-DBUILD_SHARED_LIBS=${if static then "OFF" else "ON"}"
   ] ++ lib.optionals (cxxStandard != null) [
-    "-DCMAKE_CXX_STANDARD=${toString cxxStandard}"
+    "-DCMAKE_CXX_STANDARD=${cxxStandard}"
   ];
 
   nativeBuildInputs = [ cmake ];

pkgs/development/libraries/grpc/default.nix

···
     "-DCMAKE_SKIP_BUILD_RPATH=OFF"
   ] ++ lib.optionals (stdenv.hostPlatform != stdenv.buildPlatform) [
     "-D_gRPC_PROTOBUF_PROTOC_EXECUTABLE=${buildPackages.protobuf}/bin/protoc"
-  ] ++ lib.optionals
-    ((stdenv.hostPlatform.useLLVM or false) && lib.versionOlder stdenv.cc.cc.version "11.0") [
+  ] ++ lib.optionals ((stdenv.hostPlatform.useLLVM or false) && lib.versionOlder stdenv.cc.cc.version "11.0") [
     # Needs to be compiled with -std=c++11 for clang < 11. Interestingly this is
     # only an issue with the useLLVM stdenv, not the darwin stdenv…
     # https://github.com/grpc/grpc/issues/26473#issuecomment-860885484

pkgs/top-level/all-packages.nix

···
 
   or-tools = callPackage ../development/libraries/science/math/or-tools {
     python = python3;
-    abseil-cpp = abseil-cpp.override { static = true; };
+    # or-tools builds with -std=c++17, so abseil-cpp must
+    # also be built that way
+    abseil-cpp = abseil-cpp.override {
+      static = true;
+      cxxStandard = "17";
+    };
   };
 
   rubiks = callPackage ../development/libraries/science/math/rubiks { };