Support for the exception specifications using types was removed in
C++17 (and "throw ()" in C++20), so don't use them when using the C++
compiler any longer, as this broke the example with recent g++ versions
that use C++17 by default.
We still need them for SWIG, however, so use SWIG_THROW macro, defined
differently for SWIG and the compiler, to preserve the existing
behaviour.
Using %except might be a better idea, but would require more changes.
