Handle static unwinder in ltoDepsMutator

The implementation before libraryDependencyTag was added failed to
treat the libgcc_unwind dependency as a static library when traversing
dependencies for LTO because it didn't handle staticUnwinderDepTag.

Bug: 162437057
Test: m checkbuild
Change-Id: Iccc96c0daa0379f51eb975c51fd5e8c507a0daba