[libclang] Make sure Preprocessor is set in ASTUnit during indexing.

llvm-svn: 148319
diff --git a/clang/tools/libclang/Indexing.cpp b/clang/tools/libclang/Indexing.cpp
index 630c55b..6bffc6b 100644
--- a/clang/tools/libclang/Indexing.cpp
+++ b/clang/tools/libclang/Indexing.cpp
@@ -176,6 +176,7 @@
     IndexCtx.setASTContext(CI.getASTContext());
     Preprocessor &PP = CI.getPreprocessor();
     PP.addPPCallbacks(new IndexPPCallbacks(PP, IndexCtx));
+    IndexCtx.setPreprocessor(PP);
     return new IndexingConsumer(IndexCtx);
   }