Fix FORTIFY_SOURCE warnings from gcc in Debug mode

CMakeLists.txt

@@ -299,7 +299,10 @@ 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")
+  set(cflags "-Wall -Wextra -Wpointer-arith -Winvalid-pch -Wcast-align -Wwrite-strings")
+  if(CMAKE_BUILD_TYPE STREQUAL "Release" OR CMAKE_BUILD_TYPE STREQUAL "RelWithDebInfo")
+    set(cflags "${cflags} -D_FORTIFY_SOURCE=2")
+  endif()
 
   ctkFunctionCheckCompilerFlags("-fdiagnostics-show-option" cflags)
   ctkFunctionCheckCompilerFlags("-Wl,--no-undefined" cflags)