I would have thought 

```
if(USE_APR)
  find_package(APR)
  if (APR_FOUND AND APR_UTIL_FOUND)
    add_definitions (-D_USE_APR)
    include_directories(${APR_INCLUDE_DIR})
    link_directories(${APR_LIBRARIES})
  else()
    message(FATAL_ERROR "APR requested but package not found")
  endif()
else()
  add_definitions (-D_NO_APR)
endif(USE_APR)
```