Nailed it! Thanks to this post I discovered that evolution-data-server doesn't build libexchange-storage by default because the libexchange libraries are dependent on openldap - and by default evolution-data-server doesn't link with openldap. Thanks a lot. To fix the problem I needed to build evolution-data-server again, this time specifying openldap:
sh autogen.sh --with-openldap=yes --prefix=/opt/evolution-data-server
Once I had installed the new build of evolution-data-server I could finally build evolution-exchange. Having run make install, the Exchange option was available in Evolution 2.10:
UPDATE: Unfortunately, although the Exchange option was available, there was no where to enter the OWA URL! I had to rebuild evolution with openldap enabled: sh autogen.sh --with-openldap=yes --prefix=/opt/evolution
The documentation on building Evolution is non-existent; I have been entirely dependent on forums for scraps of information. This is not so much open source as obscure source software: you can have the source code but don't expect us to help you. But why did I expect anything else? I wouldn't expect much from a small "community" based development project, but there is no getting away from the fact that Evolution is Novell's baby.
Now let's see if it works.