registers for a given virtual register.
Reserved registers are filtered from the allocation order, and any valid hint is
returned as the first suggestion.
For target dependent hints, a number of arcane target hooks are invoked.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@121497 91177308-0d34-0410-b5e6-96231b3b80d8
