Bug#561763: polyml: please add arm64 when updating

[Edmund Grimley Evans]

The upstream trunk has support for arm64 since 2015-07-13:

https://github.com/polyml/polyml/commit/9d84a491c4ec5fa95c085ddcc8f9cca84bbea870

It looks like a simple patch that might apply to the last released
version (still 5.5.2).