Lazily load the ContextDecl for a lambda's DefinitionData, to fix a
deserialization cycle caused by the ContextDecl recursively importing members
of the lambda's closure type.

llvm-svn: 279694
diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index 72b2bf6..7f9ae8d 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -5565,7 +5565,7 @@
     Record->push_back(Lambda.NumCaptures);
     Record->push_back(Lambda.NumExplicitCaptures);
     Record->push_back(Lambda.ManglingNumber);
-    AddDeclRef(Lambda.ContextDecl);
+    AddDeclRef(D->getLambdaContextDecl());
     AddTypeSourceInfo(Lambda.MethodTyInfo);
     for (unsigned I = 0, N = Lambda.NumCaptures; I != N; ++I) {
       const LambdaCapture &Capture = Lambda.Captures[I];