[clang-shlib] Fix clang-shlib for PRIVATE dependencies

Any static library with a PRIVATE dependency ends up with a
$<LINK_ONLY:...> generator expression in its INTERFACE_LINK_LIBRARIES,
which won't be evaluated by the $<TARGET_PROPERTY:...>, so we end up
with an unevaluated generator expression in the generated build file and
Ninja chokes on the dollar sign. Just use the static library directly
for its dependencies instead of trying to propagate dependencies
manually.

Differential Revision: https://reviews.llvm.org/D64579

llvm-svn: 365825