Handle out being a symlink

Soong needs to be able to reverse the relative path to out. Switch to
absolute paths if .. won't work because of out being a symlink to
somewhere else.

Bug: 27612837
Change-Id: Ib8b9e0f80523148cfd4b69a03d164578916d8fd5
(cherry picked from commit d53c0c7b)
[ccross: resolved conflicts in nyc-dev]