Undo a bit of fcf4e360 that confuses MSVC

clang\lib\Serialization\GlobalModuleIndex.cpp(818): error C2440: 'initializing': cannot convert from 'const ValueTy' to '_Ty2 &&'
        with
        [
            ValueTy=llvm::SmallVector<unsigned int,2>
        ]
        and
        [
            _Ty2=llvm::SmallVector<unsigned int,2>
        ]