Use CMAKE_{C,CXX}_FLAGS_INIT variable when initializing CTK_{C,CXX}_FLAGS

CMakeLists.txt

@@ -239,8 +239,8 @@ ENDIF()
 #-----------------------------------------------------------------------------
 # CTK C/CXX Flags
 #
-SET(CTK_C_FLAGS "${COVERAGE_C_FLAGS} ${ADDITIONAL_C_FLAGS}")
-SET(CTK_CXX_FLAGS "${VISIBILITY_CXX_FLAGS} ${COVERAGE_CXX_FLAGS} ${ADDITIONAL_CXX_FLAGS}")
+SET(CTK_C_FLAGS "${CMAKE_C_FLAGS_INIT} ${COVERAGE_C_FLAGS} ${ADDITIONAL_C_FLAGS}")
+SET(CTK_CXX_FLAGS "${CMAKE_CXX_FLAGS_INIT} ${VISIBILITY_CXX_FLAGS} ${COVERAGE_CXX_FLAGS} ${ADDITIONAL_CXX_FLAGS}")
 
 IF(CMAKE_COMPILER_IS_GNUCXX)
   SET(cflags "-Wall -Wextra -Wpointer-arith -Winvalid-pch -Wcast-align -Wwrite-strings -D_FORTIFY_SOURCE=2")