Merge remote-tracking branch 'origin/swift-4.0-branch' into stable

* origin/swift-4.0-branch:
  [c-index-test] CMake: add missing reference to clangSerialization library.
  [index] CMake: add missing reference to clangSerialization library.
  [c-index-test] Provide capability to index module file imports and dump their input files.
  [c-index-test] Provide capability for 'c-index-test core' to dump symbol information from a PCH/module file.