Revert rL348121 from llvm/trunk: [NFC][AArch64] Split out backend features
This patch splits backend features currently
hidden behind architecture versions.
For example, currently the only way to activate
complex numbers extension is targeting an v8.3
architecture, where after the patch this extension
can be added separately.
This refactoring is required by the new command lines proposal:
Reviewers: DavidSpickett, olista01, t.p.northover
Subscribers: kristof.beyls, bryanpkc, javed.absar, pbarrio
Differential revision: https://reviews.llvm.org/D54633
This has been causing buildbots failures for the past 24 hours: http://lab.llvm.org:8011/builders/llvm-clang-x86_64-expensive-checks-win/builds/14386