LiveStacks: Rename LiveStack.{h|cpp} to LiveStacks.{h|cpp}; NFC

Filenames should match the name of the class they contain.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@321037 91177308-0d34-0410-b5e6-96231b3b80d8
11 files changed