Update CMakeLists.txt

Author: flexferrum

CMakeLists.txt

@@ -36,7 +36,7 @@ else ()
             set (MSVC_RUNTIME_TYPE "/MD")
         endif ()
     endif ()
-    set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${MSVC_RUNTIME_TYPE}")
+    set (CMAKE_CXX_FLAGS_${CMAKE_BUILD_TYPE} "${CMAKE_CXX_FLAGS_${CMAKE_BUILD_TYPE}} ${MSVC_RUNTIME_TYPE}")
 endif()
 
 if("${GTEST_ROOT}" STREQUAL "" AND WITH_TESTS)