message: Fix assertion in 6.0
diff: @@ -2492,7 +2492,6 @@ void
  Module::execPreprocessor(const char *infilename, llvm::raw_string_ostream *ostream) const
  {
  clang::CompilerInstance inst;
  - inst.createFileManager();
  llvm::raw_fd_ostream stderrRaw(2, false);
  @@ -2506,6 +2505,8 @@ Module::execPreprocessor(const char *infilename, llvm::raw_string_ostream *ostre
  inst.setDiagnostics(diagEngine);
  + inst.createFileManager();
  +
  #if ISPC_LLVM_VERSION <= ISPC_LLVM_3_4 // 3.2, 3.3, 3.4
  clang::TargetOptions &options = inst.getTargetOpts();
  #else // LLVM 3.5+
  