[compiler-rt] Partially revert 8bd2722f

Don't normalize arm architecture names; doing that loses the ability
to pick the right implementation of builtins for each architecture
variant. When building compiler-rt builtins as part of a
runtimes build, builtins for multiple armv* variants could be built
in the same directory, and with the simplified architecture name,
they'd all be built in the same directory, overlapping each other.