Silence MSVC warning on 'uint16_t |= bool' with a cast

This isn't C4800, it's C4805.  MSVC says this is unsafe, but it
generates correct code.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200229 91177308-0d34-0410-b5e6-96231b3b80d8