Re-land r301697 "[IR] Make add/remove Attributes use AttrBuilder instead of AttributeList"

This time, I fixed, built, and tested clang.

This reverts r301712.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@301981 91177308-0d34-0410-b5e6-96231b3b80d8
12 files changed