Build failure on debian-jessie

[mkoeppe]

With #107 applied, on debian-jessie, another build problem becomes visible (https://github.com/mkoeppe/primesieve/runs/4342272471?check_suite_focus=true):

/sage/local/var/tmp/sage/build/primesieve-git/src/src/iterator.cpp:34:11: error: function 'primesieve::iterator& primesieve::iterator::operator=(primesieve::iterator&&)' defaulted on its redeclaration with an exception-specification that differs from the implicit declaration 'primesieve::iterator& primesieve::iterator::operator=(primesieve::iterator&&)'
 iterator& iterator::operator=(iterator&&) noexcept = default;
           ^

https://stackoverflow.com/questions/47032077/noexcept-default-compilation-error

[kimwalisch]

Wontfix, see: #107