c++: remove i_c_e_p parm from tsubst_copy_and_build

c++: remove i_c_e_p parm from tsubst_copy_and_build

It seems the only and original purpose of tsubst_copy_and_build's
integral_constant_expression_p boolean parameter (added in r116276, which
predates the constexpr machinery) is to diagnose certain constructs that
aren't allowed to appear in a C++98 integral constant expression
context, specifically casts to a non-integral type (diagnosed from the
*_CAST_EXPR case of tsubst_copy_and_build) or dependent names that
resolve to a non-constant decl (diagnosed from the IDENTIFIER_NODE case
of tsubst_copy_and_build).  The parameter has no effect outside of C++98
AFAICT.

But diagnosing such constructs should arguably be the job of the constexpr
machinery (e.g. is_constant_expression) after substitution, and doing it
during substitution by way of an additional parameter complicates the
API of this workhorse function for what amounts to a couple of archaic
C++98 restrictions.  And it seems is_constant_expression already does a
good job of diagnosing the aforementioned two constructs in C++98 mode,
at least as far as our testsuite is concerned.

So this patch removes this parameter from tsubst_copy_and_build,
tsubst_expr and tsubst_copy_and_build_call_args.  The only interesting
changes are to potential_constant_expression_1 and the IDENTIFIER_NODE
and *_CAST_EXPR cases of tsubst_copy_and_build; the rest are mechanical
adjustments to the functions' signatures and their call sites.

gcc/cp/ChangeLog:

	* constexpr.cc (potential_constant_expression_1)
	<case *_CAST_EXPR>: Use
	cast_valid_in_integral_constant_expression_p instead of
	open coding it.
	* constraint.cc (tsubst_valid_expression_requirement): Adjust
	calls to tsubst_copy_and_build and tsubst_expr.
	(tsubst_constraint): Likewise.
	(satisfy_atom): Likewise.
	(diagnose_trait_expr): Likewise.
	* cp-tree.h (tsubst_copy_and_build): Remove i_c_e_p parameter.
	(tsubst_expr): Likewise.
	* init.cc (get_nsdmi): Adjust calls to tsubst_copy_and_build
	and tsubst_expr.
	* pt.cc (expand_integer_pack): Likewise.
	(instantiate_non_dependent_expr_internal): Likewise.
	(tsubst_friend_function): Likewise.
	(tsubst_attribute): Likewise.
	(instantiate_class_template): Likewise.
	(tsubst_template_arg): Likewise.
	(gen_elem_of_pack_expansion_instantiation): Likewise.
	(tsubst_fold_expr_init): Likewise.
	(tsubst_pack_expansion): Likewise.
	(tsubst_default_argument): Likewise.
	(tsubst_function_decl): Likewise.
	(tsubst_decl): Likewise.
	(tsubst_arg_types): Likewise.
	(tsubst_exception_specification): Likewise.
	(tsubst): Likewise.
	(tsubst_init): Likewise.
	(tsubst_copy): Likewise.
	(tsubst_omp_clause_decl): Likewise.
	(tsubst_omp_clauses): Likewise.
	(tsubst_copy_asm_operands): Likewise.
	(tsubst_omp_for_iterator): Likewise.
	(tsubst_expr): Likewise.  Remove i_c_e_p parameter.
	(tsubst_omp_udr): Likewise.
	(tsubst_non_call_postfix_expression): Likewise.  Remove i_c_e_p parameter.
	(tsubst_lambda_expr): Likewise.
	(tsubst_copy_and_build_call_args): Likewise.
	(tsubst_copy_and_build): Likewise.  Remove i_c_e_p parameter.
	<case IDENTIFIER_NODE>: Adjust call to finish_id_expression
	following removal of i_c_e_p.
	<case *_CAST_EXPR>: Remove C++98-specific cast validity check
	guarded by i_c_e_p.
	(maybe_instantiate_noexcept): Adjust calls to
	tsubst_copy_and_build and tsubst_expr.
	(instantiate_body): Likewise.
	(instantiate_decl): Likewise.
	(tsubst_initializer_list): Likewise.
	(tsubst_enum): Likewise.

gcc/objcp/ChangeLog:

	* objcp-lang.cc (objcp_tsubst_copy_and_build): Adjust calls to
	tsubst_copy_and_build and tsubst_expr.

gcc/testsuite/ChangeLog:

	* g++.dg/template/crash55.C: Don't expect additional
	C++98-specific diagnostics.
	* g++.dg/template/ref3.C: Remove C++98-specific xfail.