I had previously installed freeradius version 2.1.3, so I just replaced the lib files from version 2.1.8 with those from version 2.1.3 (I found them in /usr/src/packages/BUILD/freeradius-server-2.1.3/src/modules/rlm_ldap/.libs/).
Files I replaced:
rlm_ldap-2.1.8 replaced with: rlm_ldap-2.1.3.so
rlm_ldap.a replaced with: rlm_ldap.a (from 2.1.3)
rlm_ldap.so -> rlm_ldap-2.1.3.so replaced with: rlm_ldap.so --> rlm_ldap-2.1.8
If you have a more recent version of freeradius (like 2.1.7), I think that the libs from this version would work too...this was just what I had easy access to.
Let me know if you need these files.