Fix the last -Wnon-pod-memset I'm seeing. This is benign, but appears

Fix the last -Wnon-pod-memset I'm seeing. This is benign, but appears
a bit more sinister as the memset doesn't do what the constructor does.
There seems to be a cleaner solution than a cast here though, instead we
can point the memset destination into the union its actually trying to
clear.

An alternative is to point to the Untyped member of this union. Review
appreciated, and if that is cleaner I'm happy to switch. All of these
should be functionally equivalent to the original code.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@130395 91177308-0d34-0410-b5e6-96231b3b80d8