gh-152216: Silence expat compiler warnings

Author: cdce8p

Makefile.pre.in

@@ -1449,7 +1449,7 @@ Modules/expat/xmlrole.o: $(srcdir)/Modules/expat/xmlrole.c $(LIBEXPAT_HEADERS) $
 	$(CC) -c $(LIBEXPAT_CFLAGS) -o $@ $(srcdir)/Modules/expat/xmlrole.c
 
 Modules/expat/xmltok.o: $(srcdir)/Modules/expat/xmltok.c $(LIBEXPAT_HEADERS) $(PYTHON_HEADERS)
-	$(CC) -c $(LIBEXPAT_CFLAGS) -o $@ $(srcdir)/Modules/expat/xmltok.c
+	$(CC) -Wno-unreachable-code-fallthrough -c $(LIBEXPAT_CFLAGS) -o $@ $(srcdir)/Modules/expat/xmltok.c
 
 $(LIBEXPAT_A): $(LIBEXPAT_OBJS)
 	-rm -f $@