message: Initialize the ClangImporter's clang module search path
diff: #include "clang/AST/DeclObjC.h"
  #include "clang/Basic/TargetInfo.h"
  #include "clang/Basic/TargetOptions.h"
  +#include "clang/Driver/Driver.h"
  #include "llvm/ADT/ArrayRef.h"
  #include "llvm/ADT/StringRef.h"
  #include "llvm/CodeGen/TargetSubtargetInfo.h"
  @@ -2640,6 +2641,15 @@ swift::ClangImporterOptions &SwiftASTContext::GetClangImporterOptions() {
  GetCompilerInvocation().getClangImporterOptions();
  if (!m_initialized_clang_importer_options) {
  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();
  +
  FileSpec clang_dir_spec;
  if (HostInfo::GetLLDBPath(ePathTypeClangDir, clang_dir_spec))
  clang_importer_options.OverrideResourceDir =
  