fix build on non-jit arches
Build on non-jit arch like s390 fails with
[translation:info] Translating target as defined by targetpypystandalone
[platform:msg] Setting platform to 'host' cc=None
Traceback (most recent call last):
File "translate.py", line 322, in <module>
main()
File "translate.py", line 208, in main
targetspec_dic, translateconfig, config, args = parse_options_and_load_target()
File "translate.py", line 176, in parse_options_and_load_target
targetspec_dic['handle_config'](config, translateconfig)
File "targetpypystandalone.py", line 109, in handle_config
raise Exception("You have to specify the --opt level.\n"
Exception: You have to specify the --opt level.
Try --opt=2 or --opt=jit, or equivalently -O2 or -Ojit .