fix & suppress warnings of generated code

src/Gui/SelectionFilter.cpp

@@ -347,7 +347,15 @@ int SelectionFilterlex(void);
 
 #ifndef DOXYGEN_SHOULD_SKIP_THIS
 // Scanner, defined in SelectionFilter.l
+#if defined(__clang__)
+# pragma clang diagnostic push
+# pragma clang diagnostic ignored "-Wsign-compare"
+# pragma clang diagnostic ignored "-Wunneeded-internal-declaration"
+#endif
 #include "lex.SelectionFilter.c"
+#if defined(__clang__)
+# pragma clang diagnostic pop
+#endif
 #endif // DOXYGEN_SHOULD_SKIP_THIS
 }