cmd/link: add DW_AT_go_runtime_type to unsafe.Pointer and fix it for

cmd/link: add DW_AT_go_runtime_type to unsafe.Pointer and fix it for
uintptr

Adds the DW_AT_go_runtime_type attribute to the debug_info entry for
unsafe.Pointer (which is special) and fixes the debug_info entry of
uintptr so that its DW_AT_go_runtime_type attribute has the proper
class (it was accidentally using DW_CLS_ADDRESS instead of
DW_CLS_GO_TYPEREF)

Change-Id: I52e18593935fbda9bc425e849f4c7f50e9144ad4
Reviewed-on: https://go-review.googlesource.com/c/go/+/558275
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>