ADT/PointerIntPairTest.cpp: Appease msc17.

  - Use constructor instead of initializer list.
  - Disable ManyUnusedBits for now.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203436 91177308-0d34-0410-b5e6-96231b3b80d8