fixed: make WITH_NDEBUG cmake option work again

cmake now adds -DNDEBUG to default CXX flags
invert logic and use -UNDEBUG to remove instead

cmake/Modules/UseOptimization.cmake

@@ -64,8 +64,8 @@ if (CXX_COMPAT_GCC)
   # use these options for release builds - full optimization
   add_options (ALL_LANGUAGES "${_prof_RELEASE}" ${_opt_rel} ${_opt_flags})
   option(WITH_NDEBUG "Disable asserts in release mode" ON)
-  if(WITH_NDEBUG)
-    add_options (ALL_LANGUAGES "${_prof_RELEASE}" -DNDEBUG)
+  if(NOT WITH_NDEBUG)
+    add_options (ALL_LANGUAGES "${_prof_RELEASE}" -UNDEBUG)
   endif()
 
 else ()