Removing llvm::distance and llvm::copy for iterator_range based on post-commit review feedback. Adding an explicit range-based constructor to SmallVector, which supersedes the llvm::copy functionality.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203460 91177308-0d34-0410-b5e6-96231b3b80d8