Fix libunwind dependency tracking.

This has been working so far because of ndk-build's implementation of
the STL. This is changing to have libc++ describe its own
dependencies and causes this to break as described in the comment.

Test: ndk/checkbuild.py && ndk/run_tests.py
Bug: None
Change-Id: I763a4f88a82be13c5d80e440945de3c62e399ea2
(cherry picked from commit 709eecc2972212419399b891bec947c8daa6d428)
1 file changed