This lets select sub-targets enable this pass. The patch implements the
idea from the recent llvm-dev thread:
http://thread.gmane.org/gmane.comp.compilers.llvm.devel/94925
The goal is to enable the LoopDataPrefetch pass for the Cyclone
sub-target only within Aarch64.
Positive and negative tests will be included in an upcoming patch that
enables selective prefetching of large-strided accesses on Cyclone.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@262844 91177308-0d34-0410-b5e6-96231b3b80d8