[Exim] socklen_t not defined

I need to move up to exim-4.30 to get some of the new facilities. However, I have a
compilation failure. I am working on IRIX-6 and socklen_t is not defined in
/usr/include/sys/socket.h.

Can someone suggest the best way to get round this please?

Phil.
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Phil Chambers (postmaster@???)
University of Exeter