Merge pull request #425 from redboltz/fix_424

Fixed #424.

Author: redboltz

include/CMakeLists.txt

@@ -52,8 +52,12 @@ IF (NOT MQTT_NO_TLS)
 ENDIF ()
 
 #str to list
-string(REPLACE " " ";" CHK_CXX_FLAGS ${CMAKE_CXX_FLAGS})
-string(REPLACE " " ";" CHK_ENV_CXXFLAGS $ENV{CXXFLAGS})
+IF (CMAKE_CXX_FLAGS)
+    string(REPLACE " " ";" CHK_CXX_FLAGS ${CMAKE_CXX_FLAGS})
+ENDIF ()
+IF ($ENV{CXXFLAGS})
+    string(REPLACE " " ";" CHK_ENV_CXXFLAGS $ENV{CXXFLAGS})
+ENDIF ()
 
 FOREACH (HDR ${HDR_MQTT})
     get_filename_component(HDR_WE ${HDR} NAME_WE)