All *BSDs use ${PREFIX}/{man,info} for man and info pages

Modules/GNUInstallDirs.cmake

@@ -265,7 +265,7 @@ if(NOT CMAKE_INSTALL_DATADIR)
   set(CMAKE_INSTALL_DATADIR "${CMAKE_INSTALL_DATAROOTDIR}")
 endif()
 
-if(CMAKE_SYSTEM_NAME STREQUAL "OpenBSD")
+if(CMAKE_SYSTEM_NAME MATCHES "^(.*BSD|DragonFly)$")
   if(NOT CMAKE_INSTALL_INFODIR)
     set(CMAKE_INSTALL_INFODIR "" CACHE PATH "info documentation (info)")
     set(CMAKE_INSTALL_INFODIR "info")