Use nativeBuildInputs for nix-shell

Now the nix-shell will generate a nix expression that looks like this:

with import <nixpkgs> {};
runCommand "shell" {
  nativeBuildInputs = [
    (...)
    (...)
    (...)
  ];
}

from

$ nix-shell --packages ... ... ...

Fixes the issue described in NixOS/nixpkgs#38657.

src/nix-build/nix-build.cc

@@ -328,7 +328,7 @@ int main(int argc, char ** argv)
         if (packages) {
             instArgs.push_back("--expr");
             std::ostringstream joined;
-            joined << "with import <nixpkgs> { }; runCommand \"shell\" { buildInputs = [ ";
+            joined << "with import <nixpkgs> { }; runCommand \"shell\" { nativeBuildInputs = [ ";
             for (const auto & i : exprs)
                 joined << '(' << i << ") ";
             joined << "]; } \"\"";