Astshim build on OpenSuse

Thought this might be useful for OpenSuse or similar Linux flavor users.

If astshim fails (cannot find .so shared libraries), a link should be made manually under
ln -sf lib64 lib

This is somewhat related to:

I think the answer is to fix starlink_ast the same way we fixed it for GSL. That is, add --libdir explicitly. @rowen I think that will work since it’s all autoconf.

Implemented as