re PR c++/18905 (Strange error: subscripted value is neither array nor pointer)

cp:
	PR c++/18905
	* cp-tree.h (integral_constant_value): Declare.
	* call.c (null_ptr_cst_p): Use integral_constant_value, not
	decl_constant_value.
	(convert_like_real): Likewise.
	* class.c (check_bitfield_decl): Likewise.
	* cvt.c (ocp_convert): Likewise.
	(convert): Remove unnecessary decl_constant_value call.
	* decl.c (compute_array_index_type): Use integral_constant_value,
	not decl_constant_value.
	(build_enumerator): Likewise.
	* decl2.c (grokfield): Likewise.
	* init.c (decl_constant_value): Simplify.
	(integral_constant_value): New.
	* pt.c (fold_decl_constant_value): Use integral_constant_value,
	remove subsequent check.
	(tsubst): Use integral_constant_value, not decl_constant_value.
	(tsubst_copy, unify): Likewise.
	* typeck.c (decay_conversion): Likewise.
	(build_compound_expr): Remove unnecessary decl_constant_value
	calls.
	(build_static_cast_1, build_reinterpret_cast_1):
	(convert_for_assignment): Remove comment about not calling
	decl_constant_value.
testsuite:
	PR c++/18905
	* g++.dg/template/init4.C: New.
	* g++.dg/opt/static3.C: Enable optimizer.

From-SVN: r92257