The standard says that in a generic lambda we should speculatively capture
'this' if we see a call to an overload set that contains a non-static member
function, but it seems wrong to reject the program if we can't capture,
since it might not actually be needed.

	* lambda.c (lambda_expr_this_capture): Change add_capture_p to int.
	(maybe_generic_this_capture): Pass -1.

From-SVN: r269095