fix: add workaround so that pnpm@5 can pack regular packages

Author: paul-soporan

packages/gatsby/content/features/protocols.md

@@ -52,7 +52,7 @@ [email protected]:yarnpkg/berry.git#head=master
 
 - Yarn will use either of Yarn, npm, or pnpm to pack the repository, based on the repository style (ie we'll use Yarn if there's a `yarn.lock`, npm if there's a `package-lock.json`, or pnpm if there's a `pnpm-lock.yaml`)
 
-- Workspaces can be cloned as long as the remote repository uses Yarn, npm (npm@>=7.x has to be installed on the system), or pnpm. Just reference the workspace by name in your range (you can optionally enforce the tag as well):
+- Workspaces can be cloned as long as the remote repository uses Yarn, npm (npm@>=7.x has to be installed on the system), or pnpm (pnpm@>=6.x has to be installed on the system). Just reference the workspace by name in your range (you can optionally enforce the tag as well):
 
 ```
 [email protected]:yarnpkg/berry.git#workspace=@yarnpkg/shell&tag=@yarnpkg/shell/2.1.0

packages/yarnpkg-core/sources/scriptUtils.ts

@@ -350,10 +350,6 @@ export async function prepareExternalProject(cwd: PortablePath, outputPath: Port
           }],
 
           [PackageManager.Pnpm, async () => {
-            const workspaceCli = workspace !== null
-              ? [`--filter`, workspace]
-              : [];
-
             const install = await execUtils.pipevp(`pnpm`, [`install`], {cwd, env, stdin, stdout, stderr, end: execUtils.EndStrategy.ErrorCode});
             if (install.code !== 0)
               return install.code;
@@ -368,7 +364,10 @@ export async function prepareExternalProject(cwd: PortablePath, outputPath: Port
 
             // - `pnpm pack` doesn't support the `--filter` flag so we have to use `pnpm exec`
             // - We have to use the `--pack-destination` flag because otherwise pnpm generates the tarball inside the workspace cwd
-            const packArgs = [...workspaceCli, `exec`, `pnpm`, `pack`, `--pack-destination`, npath.fromPortablePath(cwd)];
+            // - Only pnpm@>=6.x supports the `--pack-destination` flag (and previous versions throw an error)
+            const packArgs = workspace !== null
+              ? [`--filter`, workspace, `exec`, `pnpm`, `pack`, `--pack-destination`, npath.fromPortablePath(cwd)]
+              : [`pack`];
 
             const pack = await execUtils.pipevp(`pnpm`, packArgs, {cwd, env, stdin, stdout: packStream, stderr});
             if (pack.code !== 0)