libraries lack a soname

[Alessandro-Barbieri]

see https://bugs.gentoo.org/850424
log https://850424.bugs.gentoo.org/attachment.cgi?id=783362

 * QA Notice: The following shared libraries lack a SONAME
 * /usr/lib64/libcmepoll.so
 * /usr/lib64/libcmmulticast.so
 * /usr/lib64/libcmselect.so
 * /usr/lib64/libcmsockets.so
 * /usr/lib64/libcmudp.so

[eisenhauer]

These transports are generally used via dlopen(), rather than being linked directly into applications. At least to my understanding, SONAMEs are handled differently on different platforms and in some situations you need to specify it in the dlopen(). I'm guessing that addressing this would require changes in the evpath transport search mechanism and/or changes in how the transport is specified. Given the pretty static nature of the api between evpath and the transports, I think there's little to gain from this, so while I'd consider a PR, this isn't a high priority.