FindCerf: add message to neutralize 'Cerf not found'

cmake/find/FindCerf.cmake

@@ -45,6 +45,7 @@ if(Cerf_FOUND)
     set(Cerf_IS_CPP OFF CACHE BOOL "Define whether CERF shall be used as C++")
 else()
     # C version not found and cache is empty => search for C++ version
+    message("Since we did not find the C version of libcerf, we will now search the C++ version")
     unset(Cerf_FOUND)
     unset(Cerf_LIBRARIES)
     find_library(Cerf_LIBRARIES NAMES cerfcpp)