Simplifying Triple::parseARMArch, leaving all the parsing to ARMTargetParser.
This commit also adds AArch64 detection to ARMTargetParser canonicalization,
and a two RedHat arch names (v{6,7}hl, meaning hard-float / little-endian).
Adding enough unit tests to cover the basics. Clang checks fine.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@237902 91177308-0d34-0410-b5e6-96231b3b80d8