symlinkJoin doesn't work on WSL

Build 16257

Nixpkgs ghcWithPackages fails because symlinkJoin doesn't work. See https://github.com/NixOS/nixpkgs/issues/26506

To reproduce, install nix, then using nix try to install ghc with packages. For example:

• curl https://nixos.org/nix/install | sh
• echo "{}: {foo=(import {}).haskellPackages.ghcWithPackages (h: [h.text]);}" > foo.nix
• nix-env -f foo.nix -i -A foo

The following errors are produced:

installing ‘ghc-8.0.2-with-packages’
these derivations will be built:
  /nix/store/b8vq8x4zf7064k03br4arzwxq17q9ccn-ghc-8.0.2-with-packages.drv
building path(s) ‘/nix/store/6ngxwi2xpnzcivvkwiy78cjg09r9f1mc-ghc-8.0.2-with-packages’
.: File exists
..: File exists
.: File exists
..: File exists
lib: /nix/store/gyw8sz9pmg34hpwxs5rz1g90q8fvia3q-text-1.2.2.1/lib
share: /nix/store/gyw8sz9pmg34hpwxs5rz1g90q8fvia3q-text-1.2.2.1/share
rm: cannot remove '/nix/store/6ngxwi2xpnzcivvkwiy78cjg09r9f1mc-ghc-8.0.2-with-packages/bin/ghc': Permission denied
builder for ‘/nix/store/b8vq8x4zf7064k03br4arzwxq17q9ccn-ghc-8.0.2-with-packages.drv’ failed with exit code 1
error: build of ‘/nix/store/b8vq8x4zf7064k03br4arzwxq17q9ccn-ghc-8.0.2-with-packages.drv’ failed

Start by reproducing the documented nix-env commands on WSL and inspect the reported symlinkJoin errors, including the permission failure when removing the ghc link. Done means ghcWithPackages installs successfully on WSL without the File exists or Permission denied errors.