Added cmake settable property to enable the macro

CMakeLists.txt

@@ -449,6 +449,11 @@ SET_SOURCE_FILES_PROPERTIES(ProcessUNIX.c System.c PROPERTIES
   COMPILE_FLAGS "-DKWSYS_C_HAS_PTRDIFF_T=${KWSYS_C_HAS_PTRDIFF_T} -DKWSYS_C_HAS_SSIZE_T=${KWSYS_C_HAS_SSIZE_T}"
   )
 
+IF(DEFINED KWSYS_PROCESS_USE_SELECT)
+  GET_PROPERTY(ProcessUNIX_FLAGS SOURCE ProcessUNIX.c PROPERTY COMPILE_FLAGS)
+  SET_PROPERTY(SOURCE ProcessUNIX.c PROPERTY COMPILE_FLAGS "${ProcessUNIX_FLAGS} -DKWSYSPE_USE_SELECT=${KWSYSPE_USE_SELECT}")
+ENDIF()
+
 IF(KWSYS_USE_DynamicLoader)
   GET_PROPERTY(KWSYS_SUPPORTS_SHARED_LIBS GLOBAL PROPERTY TARGET_SUPPORTS_SHARED_LIBS)
   IF(KWSYS_SUPPORTS_SHARED_LIBS)