c++/modules: stream TREE_UNAVAILABLE and LAMBDA_EXPR_REGEN_INFO

gcc/cp/ChangeLog:

	* module.cc (trees_out::core_bools): Stream TREE_UNAVAILABLE.
	(trees_in::core_bools): Likewise.
	(trees_out::core_vals): Stream LAMBDA_EXPR_REGEN_INFO.
	(trees_in::core_vals): Likewise.

Reviewed-by: Jason Merrill <jason@redhat.com>