libthr: Fix LIBPTHREAD_QUEUE_FIFO range

[aokblast]

Summary

LIBPTHREAD_QUEUE_FIFO is used in bitwise offset, we set the limit to
0~31 so that it won't cause undefined behavior. Also, create a new help
function to do getnv+strtol directly and check the boundary of the valid
value.

[kib]

In the summary:

Also, create a new helpER
function to do getEnv+strtol directly

lib/libthr/thread/thr_init.c

489

490

Why do we need to preserve errno?