[libclang]: Honor LIBCLANG_NOTHREADS for clang_parseTranslationUnit*

[nik]

Summary

Looks like this one was forgotten for clang_parseTranslationUnit*, as
LIBCLANG_NOTHREADS is checked for/in:

clang_saveTranslationUnit()
clang_reparseTranslationUnit()
clang_codeCompleteAt()
clang_indexTranslationUnit()
clang_indexSourceFile()

[bkramer]

lg

[nik]

Please submit as I do not have the necessary permissions.

cfe/trunk/tools/libclang/CIndex.cpp

if (num_unsaved_files && !unsaved_files)
     return CXError_InvalidArguments;
 
   CXErrorCode result = CXError_Failure;
   auto ParseTranslationUnitImpl = [=, &result] {
     result = clang_parseTranslationUnit_Impl(
         CIdx, source_filename, command_line_args, num_command_line_args,
         llvm::makeArrayRef(unsaved_files, num_unsaved_files), options, out_TU);
   };
+
+  if (getenv("LIBCLANG_NOTHREADS")) {
+    ParseTranslationUnitImpl();
+    return result;
+  }
+
   llvm::CrashRecoveryContext CRC;
 
   if (!RunSafely(CRC, ParseTranslationUnitImpl)) {
     fprintf(stderr, "libclang: crash detected during parsing: {\n");
     fprintf(stderr, "  'source_filename' : '%s'\n", source_filename);
     fprintf(stderr, "  'command_line_args' : [");
     for (int i = 0; i != num_command_line_args; ++i) {
       if (i)