libclang: factor out the frequent pattern static_cast<ASTUnit *>(TU->TUData)
into a getter cxtu::getASTUnit(TU)

llvm-svn: 173585
diff --git a/clang/tools/libclang/IndexingContext.cpp b/clang/tools/libclang/IndexingContext.cpp
index 2dea757..9129e92 100644
--- a/clang/tools/libclang/IndexingContext.cpp
+++ b/clang/tools/libclang/IndexingContext.cpp
@@ -196,11 +196,11 @@
 
 void IndexingContext::setASTContext(ASTContext &ctx) {
   Ctx = &ctx;
-  static_cast<ASTUnit*>(CXTU->TUData)->setASTContext(&ctx);
+  cxtu::getASTUnit(CXTU)->setASTContext(&ctx);
 }
 
 void IndexingContext::setPreprocessor(Preprocessor &PP) {
-  static_cast<ASTUnit*>(CXTU->TUData)->setPreprocessor(&PP);
+  cxtu::getASTUnit(CXTU)->setPreprocessor(&PP);
 }
 
 bool IndexingContext::isFunctionLocalDecl(const Decl *D) {