Style cleanup of old gc.root lowering code

Style cleanup of old gc.root lowering code

Use static functions for helpers rather than static member functions.  a) this changes the linking (minor at best), and b) this makes it obvious no object state is involved.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@226198 91177308-0d34-0410-b5e6-96231b3b80d8