tests: Migrated refcnt.cc test from src/unitttest to a gtest

refcnt.cc was previously tested in src/unittest/refcnttest.cc. This has
now been translated into a GTest as faithfully to the original as
possible.

Change-Id: I51f7a3d1e0a85b128c4eebd97cfe79b87406dc29
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/21499
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>
3 files changed