message: Thread the clang module cache option through to Swift
diff: @@ -2641,12 +2641,10 @@ swift::ClangImporterOptions &SwiftASTContext::GetClangImporterOptions() {
  m_initialized_clang_importer_options = true;
  // Set the Clang module search path.
  - llvm::SmallString<128> Path;
  - // FIXME: This should be querying
  - // target.GetClangModulesCachePath(), but most of the times there
  - // is no target available when this function is called.
  - clang::driver::Driver::getDefaultModuleCachePath(Path);
  - clang_importer_options.ModuleCachePath = Path.str();
  + llvm::SmallString<128> path;
  + auto props = ModuleList::GetGlobalModuleListProperties();
  + props.GetClangModulesCachePath().GetPath(path);
  + clang_importer_options.ModuleCachePath = path.str();
  FileSpec clang_dir_spec;
  if (HostInfo::GetLLDBPath(ePathTypeClangDir, clang_dir_spec))
  