re PR c++/42370 ([C++0x][lambda] in a void function: "Warning: control reaches end of non-void function")

	PR c++/42370
	* decl2.c (change_return_type): New fn.
	* semantics.c (apply_lambda_return_type): Use it.
	* cp-tree.h: Declare it.

From-SVN: r156634