[cxx-interop] Update tests for foreign reference types
This fixes errors in tests:
```
/home/build-user/swift/test/Interop/Cxx/foreign-reference/Inputs/singleton.h:8:14: error: 'operator new' is missing exception specification 'noexcept'
inline void *operator new(size_t, void *p) { return p; }
^
/usr/lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/new:173:33: note: previous declaration is here
_GLIBCXX_NODISCARD inline void* operator new(std::size_t, void* __p) _GLIBCXX_USE_NOEXCEPT
```
