Many targets have already migrated to the per-target runtime directory
layout, which is generally preferred. For AIX however, we are currently
using per-target runtime directories by default for some runtimes (i.e.
`flang-rt`) but not others. This change makes things consistent for
other runtimes (most primarily `compiler-rt`) as well, adopting the
layout uniformly for the AIX target.
This change also normalizes the triple used for building compiler-rt to
remove any OS version number, as there is currently no need to version
the runtimes this way and the driver code doesn't expect this anyhow.
224ec839a4