fix unittests build on mingw64

cmake/unittests.cmake

@@ -60,6 +60,10 @@ if (REPERTORY_ENABLE_TESTING)
     )
   endif()
 
+  target_compile_definitions(unittests PUBLIC 
+    REPERTORY_TESTING
+  )
+
   target_include_directories(unittests PUBLIC
     ${GTEST_INCLUDE_DIRS}
     ${CMAKE_CURRENT_SOURCE_DIR}/tests