Implemented support for testing the ASTImporter's
ability to generate code that CodeGen likes.  Test
cases can use this functionality by calling

// RUN: %clang_cc1 -emit-obj -o /dev/null -ast-merge %t.1.ast -ast-merge %t.2.ast %s

llvm-svn: 236011
diff --git a/clang/lib/CodeGen/CodeGenAction.cpp b/clang/lib/CodeGen/CodeGenAction.cpp
index 60aac07..b06fe42 100644
--- a/clang/lib/CodeGen/CodeGenAction.cpp
+++ b/clang/lib/CodeGen/CodeGenAction.cpp
@@ -79,6 +79,11 @@
     }
 
     void Initialize(ASTContext &Ctx) override {
+      if (Context) {
+        assert(Context == &Ctx);
+        return;
+      }
+        
       Context = &Ctx;
 
       if (llvm::TimePassesIsEnabled)