[debug flags] Address file path escape issue on Windows

[adithyabsk]

Checklist

• I have filed an issue about this change and discussed potential changes with the maintainers.
• I have received the approval from the maintainers to make this change.
• This is not a stylistic, refactoring, or cleanup change.

Please note that the maintainers will not be reviewing this change until all checkboxes are ticked. See
the Contributions section in the README for more
details.

Discussion thread for this change

Issue number: #7292

Description of this change

Adds quotes around paths passed to -fdebug-compilation-dir=

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[LeFrosch]

Shouldn't quotes alone be enough, since WorkspaceRoot.toString should return a valid path on Windows after all?