Use LIBCLANG_NOTHREADS instead of CINDEXTEST_NOTHREADS inside libclang,
so the c-index-test one can be enabled without affecting libclang.

llvm-svn: 143288
diff --git a/clang/tools/libclang/Indexing.cpp b/clang/tools/libclang/Indexing.cpp
index d05995c..7f296ae 100644
--- a/clang/tools/libclang/Indexing.cpp
+++ b/clang/tools/libclang/Indexing.cpp
@@ -407,7 +407,7 @@
                                     num_command_line_args, unsaved_files,
                                     num_unsaved_files, out_TU, TU_options, 0 };
 
-  if (getenv("CINDEXTEST_NOTHREADS")) {
+  if (getenv("LIBCLANG_NOTHREADS")) {
     clang_indexTranslationUnit_Impl(&ITUI);
     return ITUI.result;
   }