Merge commit 'refs/pull/14909/head' of git://github.com/NixOS/nixpkgs into staging

pkgs/build-support/fetchgit/nix-prefetch-git

···
 
 if test -n "$builder"; then
     test -n "$out" -a -n "$url" -a -n "$rev" || usage
-    mkdir $out
+    mkdir -p $out
     clone_user_rev "$out" "$url" "$rev"
 else
     if test -z "$hashType"; then
···
         trap "rm -rf \"$tmpPath\"" EXIT
 
         tmpFile="$tmpPath/$(url_to_name "$url" "$rev")"
-        mkdir "$tmpFile"
+        mkdir -p "$tmpFile"
 
         # Perform the checkout.
         clone_user_rev "$tmpFile" "$url" "$rev"