As added in #124274, CPUs in this range can suffer from performance
issues with ldapur. As the gain from ldar->ldapr is expected to be
greater than the minor gain from ldapr->ldapur, this opts to avoid the
instruction under the default -mcpu=generic when the -march is less that
armv8.8 / armv9.3.
I renamed AArch64Subtarget::Others to AArch64Subtarget::Generic to be
clearer what it means.
(cherry picked from commit 6424abcd6c9c6aa8171c79d0fe0369d3a10da3d5)
3351e1b142