- Previously, `winrelease` called `bundleNimbleExe`, which tries to clone
nimble to `dist/nimble` unconditionally.
- Since nightlies source tarball bundles nimble, git couldn't clone
because `dist/nimble` was already there.
This leads to 1.0.x couldn't be built with nimble bundled.
- The fix backports the logic from Nim >= 1.2.8 which can check if
`dist/nimble` was bundled by the source archive.
With this fix we can re-enable bundling of nimble to the source
archive for 1.0.x.