[patch] Unify handling of PWD

[Rafael Espíndola]

> Hm, the problem is that those tests really should test whether PWD is taken
> into account (at least clang-check-pwd).
>
> The real fix for those tests is now to create a symlink, cd into the symlink
> directory, set PWD to the symlink path, and assert on the error messages
> that the symlinked path is taken, as that would be the breaking behavior if
> PWD was not taken.
>
> Could you please add a comment to the tests that explain this?
> // FIXME: PWD cannot be set to a different path any more; adapt the test to
> build a symlink and verify
> // correct handling of PWD by asserting that clang's error messages contain
> the symlink path instead of
> // the underlying path.

It is easier to just implement that :-) It even found a missing return
in the llvm patch :-)

> As a side note: if you put changes affecting Tooling through phabricator,
> you'll get my eternal gratitude ;)
>

http://llvm-reviews.chandlerc.com/D1335

and

http://llvm-reviews.chandlerc.com/D1336

Cheers,
Rafael