[exim] Unable to compile Exim 4.52 on OpenBSD 3.7

I've got a problem trying to compile the current version of Exim (4.52) on OpenBSD 3.7

Towards the end, when it's linking the exim binary, I get the following message:

acl.o(.text+0x211b): In function 'acl_ratelimit':
: undefined reference to 'exp'
collect2: ld returned 1 exit status
*** Error code 1

This must be a 4.52 bug as I compiled 4.51 on OpenBSD 3.7 without problems.

GTG

Gordon Ross,
Network Manager/Rheolwr Rhydwaith
Countryside Council for Wales/Cyngor Cefn Gwlad Cymru