[tom@tom:~/nixpkgs]$ nix-shell -E 'with import <nixpkgs>{}; derivation {name="fake";builder="fake";system="x86_64-linux";b=pkgs.llvmPackages_11.stdenv;}'

[nix-shell:~/nixpkgs]$ echo "$b"
/nix/store/yd21j0g0ryz73kkb07wn3frgcg6fbanq-stdenv-linux

[nix-shell:~/nixpkgs]$ unset PATH; source /nix/store/yd21j0g0ryz73kkb07wn3frgcg6fbanq-stdenv-linux/setup

[nix-shell:~/nixpkgs]$ type clang
clang is /nix/store/r1p6ni32bdvbxn2yz2n1mxx39f25w5dw-clang-wrapper-11.0.1/bin/clang