Introduce support for template instantiation of lambda
expressions. This is mostly a simple refact, splitting the main "start
a lambda expression" function into smaller chunks that are driven
either from the parser (Sema::ActOnLambdaExpr) or during AST
transformation (TreeTransform::TransformLambdaExpr). A few minor
interesting points:

  - Added new entry points for TreeTransform, so that we can
  explicitly establish the link between the lambda closure type in the
  template and the lambda closure type in the instantiation.
  - Added a bit into LambdaExpr specifying whether it had an explicit
  result type or not. We should have had this anyway.

This code is 'lightly' tested.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@150417 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/AST/StmtPrinter.cpp b/lib/AST/StmtPrinter.cpp
index 292d593..746049b 100644
--- a/lib/AST/StmtPrinter.cpp
+++ b/lib/AST/StmtPrinter.cpp
@@ -1344,9 +1344,9 @@
 
     // FIXME: Attributes
 
-    // FIXME: Suppress trailing return type if it wasn't specified in
-    // the source.
-    OS << " -> " << Proto->getResultType().getAsString(Policy);
+    // Print the trailing return type if it was specified in the source.
+    if (Node->hasExplicitResultType())
+      OS << " -> " << Proto->getResultType().getAsString(Policy);
   }
 
   // Print the body.