unix/mpconfigport.h: Allow to override stackless options from commandline.
#define MICROPY_PY_GC_COLLECT_RETVAL (1)
#define MICROPY_MODULE_FROZEN_STR (1)
+#ifndef MICROPY_STACKLESS
#define MICROPY_STACKLESS (0)
#define MICROPY_STACKLESS_STRICT (0)
+#endif
#define MICROPY_PY_OS_STATVFS (1)
#define MICROPY_PY_UTIME (1)
