[3079] Don't compile code requiring shared memory

In case it is turned off, don't link against stuff requiring shared
memory, in particular mapped segment creator in tests. It is not used,
but causes link errors, as it is in a virtual method.

src/lib/datasrc/tests/memory/zone_data_updater_unittest.cc

@@ -143,6 +143,7 @@ INSTANTIATE_TEST_CASE_P(LocalSegment, ZoneDataUpdaterTest,
                         ::testing::Values(static_cast<SegmentCreator*>(
                             &memory_segment_creator)));
 
+#ifdef USE_SHARED_MEMORY
 class MappedSegmentCreator : public SegmentCreator {
 public:
     MappedSegmentCreator(size_t initial_size =
@@ -162,7 +163,6 @@ private:
     const size_t initial_size_;
 };
 
-#ifdef USE_SHARED_MEMORY
 // There should be no initialization fiasco there. We only set int value inside
 // and don't use it until the create() is called.
 MappedSegmentCreator small_creator(4092), default_creator;