Fix up install directories

src/tmpl/yarn-project.nix.in

@@ -151,17 +151,17 @@ let
     installPhase = ''
       runHook preInstall
 
-      mkdir -p "$out/libexec/$name" "$out/bin"
-
       # Move the package contents to the output directory.
       if grep -q '"workspaces"' package.json; then
         # We can't use `yarn pack` in a workspace setup, because it only
         # packages the outer workspace.
+        mkdir -p "$out/libexec"
         mv $PWD "$out/libexec/$name"
       else
         # - If the package.json has a `files` field, only files matching those patterns are copied
         # - Otherwise all files are copied.
         yarn pack --out package.tgz
+        mkdir -p "$out/libexec/$name"
         tar xzvf package.tgz --directory "$out/libexec/$name" --strip-components=1
 
         cp .yarnrc* '@@LOCKFILE@@' "$out/libexec/$name"
@@ -180,6 +180,7 @@ let
       cd "$out/libexec/$name"
 
       # Invoke a plugin internal command to setup binaries.
+      mkdir -p "$out/bin"
       yarn nixify install-bin $out/bin
 
       # A package with node_modules doesn't need the cache