clang-cl: use -fno-rtti by default

Generating RTTI in the MS ABI is currently not supported, and the failures
are confusing to users, so let's disable it by default for now.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@202178 91177308-0d34-0410-b5e6-96231b3b80d8