Refine CMakeLists.txt (#2049)

CMakeLists.txt

@@ -80,8 +80,12 @@ if(MSVC)
 else(MSVC)
   include(CheckCXXCompilerFlag)
   check_cxx_compiler_flag("-std=c++11"    SUPPORT_CXX11)
-  set(CMAKE_C_FLAGS "-O2 -Wall -fPIC ${CMAKE_C_FLAGS}")
-  set(CMAKE_CXX_FLAGS "-O2 -Wall -fPIC -std=c++11 ${CMAKE_CXX_FLAGS}")
+  if ("${CMAKE_BUILD_TYPE}" STREQUAL "Debug")
+    add_compile_options(-Wall -fPIC -std=c++11)
+  else()
+    set(CMAKE_C_FLAGS "-O2 -Wall -fPIC ${CMAKE_C_FLAGS}")
+    set(CMAKE_CXX_FLAGS "-O2 -Wall -fPIC -std=c++11 ${CMAKE_CXX_FLAGS}")
+  endif ()
   if (CMAKE_CXX_COMPILER_ID MATCHES "GNU" AND
       CMAKE_CXX_COMPILER_VERSION VERSION_GREATER 7.0)
     set(CMAKE_CXX_FLAGS "-faligned-new ${CMAKE_CXX_FLAGS}")