Revise llvm.vectorizer.width documentation

- clarify that vectorizer.width only applies if the vectorizer decides to
  vectorize.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@182938 91177308-0d34-0410-b5e6-96231b3b80d8
Fix warning and resulting formatting issue.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@182939 91177308-0d34-0410-b5e6-96231b3b80d8