d: Construct indexes of ARRAY_TYPE using ARRAY_REF.
This is a small simplification over `((T *)&array)[index]', which also
allows eliding an unneccesary marking of TREE_ADDRESSABLE when the array
expression is a parameter or variable declaration.
gcc/d/ChangeLog:
* d-codegen.cc (build_array_index): Rename to...
(build_pointer_index): ...this.
* d-tree.h (build_array_index): Rename declaration to...
(build_pointer_index): ...this.
* expr.cc (ExprVisitor::visit (IndexExp *)): Construct indexes of
ARRAY_TYPE using ARRAY_REF.
(ExprVisitor::visit (SliceExp *)): Update.
* intrinsics.cc (expand_intrinsic_bt): Update.