c++: Move CALL_FROM_NEW_OR_DELETE_P to tree.h

c++: Move CALL_FROM_NEW_OR_DELETE_P to tree.h

As discussed with richi, we should be able to use TREE_PROTECTED for this
flag, since CALL_FROM_THUNK_P will never be set on a call to an operator new
or delete.

2020-10-01  Jason Merril  <jason@redhat.com>

gcc/cp/ChangeLog:
	* lambda.c (call_from_lambda_thunk_p): New.
	* cp-gimplify.c (cp_genericize_r): Use it.
	* pt.c (tsubst_copy_and_build): Use it.
	* typeck.c (check_return_expr): Use it.
	* cp-tree.h: Declare it.
	(CALL_FROM_NEW_OR_DELETE_P): Move to gcc/tree.h.

gcc/ChangeLog:
	* tree.h (CALL_FROM_NEW_OR_DELETE_P): Move from cp-tree.h.
	* tree-core.h: Document new usage of protected_flag.