[ Upstream commit c23587c92f6e3260fe3b82bb75b38aa2553b9468 ]

the purgatory must not rely on functions from the "old" kernel,
so we must disable kasan and friends. We also need to have a
separate copy of string.c as the default does not build memcmp
with KASAN.
Reported-by: Nkbuild test robot <lkp@intel.com>
Signed-off-by: NChristian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: NVasily Gorbik <gor@linux.ibm.com>
Signed-off-by: NVasily Gorbik <gor@linux.ibm.com>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>