add @coreutils@ to correctly use coreutils to create a profile. This is needed

for NixOS, where we might not know our PATH in advance.

scripts/nix-profile.sh.in

@@ -4,7 +4,7 @@ if test -n "$HOME"; then
     if ! test -L "$NIX_LINK"; then
         echo "creating $NIX_LINK"
         _NIX_DEF_LINK=@localstatedir@/nix/profiles/default
-        ln -s "$_NIX_DEF_LINK" "$NIX_LINK"
+        @coreutils@/ln -s "$_NIX_DEF_LINK" "$NIX_LINK"
     fi
 
     export PATH=$NIX_LINK/bin:@prefix@/bin:$PATH