fe55d3e016
The default is the same as before: MICROPY_PY_USELECT=0 and
MICROPY_PY_USELECT_POSIX=1. But now this can be easily overridden at the
make command-line using, eg:
make VARIANT=dev CFLAGS_EXTRA=-DMICROPY_PY_USELECT=1
Signed-off-by: Damien George <damien@micropython.org>