Attribute bits above 1<<30 are now encoded correctly. Additionally,
the encoding/decoding functionality has been hoisted to helper functions
in Attributes.h in an effort to help the encoding/decoding to stay in
sync with the Attribute bitcode definitions.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@157581 91177308-0d34-0410-b5e6-96231b3b80d8
