[cxx-interop] Workaround name lookup issues with namespace simd
On Apple platforms, a system module `simd` declares a `namespace simd`
under `#if defined(__cplusplus)`. This namespace defines C++ overlays of
the simd types, but these types are already refined for Swift
separately, so it's not necessary to import this namespace.
This is the same issue previously encountered for the `os` module, work
around it in the same way.
rdar://143007477
