c++: Diagnose constexpr delete [] new int; and delete new int[N]; [PR95808]

c++: Diagnose constexpr delete [] new int; and delete new int[N]; [PR95808]

This patch diagnoses delete [] new int; and delete new int[1]; in constexpr
contexts by remembering
IDENTIFIER_OVL_OP_FLAGS (DECL_NAME (fun)) & OVL_OP_FLAG_VEC
from the operator new and checking it at operator delete time.

2020-10-29  Jakub Jelinek  <jakub@redhat.com>

	PR c++/95808
	* cp-tree.h (enum cp_tree_index): Add CPTI_HEAP_VEC_UNINIT_IDENTIFIER
	and CPTI_HEAP_VEC_IDENTIFIER.
	(heap_vec_uninit_identifier, heap_vec_identifier): Define.
	* decl.c (initialize_predefined_identifiers): Initialize those
	identifiers.
	* constexpr.c (cxx_eval_call_expression): Reject array allocations
	deallocated with non-array deallocation or non-array allocations
	deallocated with array deallocation.
	(non_const_var_error): Handle heap_vec_uninit_identifier and
	heap_vec_identifier too.
	(cxx_eval_constant_expression): Handle also heap_vec_uninit_identifier
	and in that case during initialization replace it with
	heap_vec_identifier.
	(find_heap_var_refs): Handle heap_vec_uninit_identifier and
	heap_vec_identifier too.

	* g++.dg/cpp2a/constexpr-new15.C: New test.