debug/dwarf: delay array type fixup to handle type cycles

A user encountered a debug/dwarf crash when running the dwarf2json
tool (https://github.com/volatilityfoundation/dwarf2json) on a
debug-built copy of the linux kernel. In this crash, the DWARF type
reader was trying to examine the contents of an array type while that
array type was still in the process of being constructed (due to
cycles in the type graph).

To avoid such situations, this patch extends the mechanism introduced
in https://go-review.googlesource.com/18459 (which handles typedef
types) to delay fixup of array types as well.

Change-Id: I303f6ce5db1ca4bd79da3581957dfc2bfc17cc01
Reviewed-on: https://go-review.googlesource.com/c/go/+/319329


Trust: Than McIntosh <thanm@google.com>
Run-TryBot: Than McIntosh <thanm@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Yi Chou <yich@google.com>
TryBot-Result: Go Bot <gobot@golang.org>