Replace another std::set in the core of CodeGenRegister, this time with sorted arrays.

Replace another std::set in the core of CodeGenRegister, this time with sorted arrays.

The hot path through this region of code does lots of batch inserts into sets. By storing them as sorted arrays, we can defer the sorting to the end of the batch, which is dramatically more efficient. This reduces tblgen runtime by 25% on my worst-case target.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@227682 91177308-0d34-0410-b5e6-96231b3b80d8