d: Fix ICEs in the front-end when pointer size is 16-bit.

d: Fix ICEs in the front-end when pointer size is 16-bit.

In the lowering of `bt*' intrinsics, some integer constants had
mismatched types, and bitsize was set to the wrong value.

In base_vtable_offset, the base offset value was calculated incorrectly.
The TypeInfo_Class object is comprised of 18 pointers and 1 uint field,
so now the internal classinfo type size is used instead.

gcc/d/ChangeLog:

	* d-target.cc (Target::_init): Don't set classinfosize.
	* d-tree.h (base_vtable_offset): Move under typeinfo.cc section.
	* decl.cc (base_vtable_offset): Move to...
	* typeinfo.cc (base_vtable_offset): ...here.  Get base offset from
	internal TypeInfo_Class type.
	* intrinsics.cc (expand_intrinsic_bt): Use pointer TYPE_SIZE for
	setting bitsize value.  Build integer constants of correct type.