- Only retry on EAGAIN, ENOMEM or EINTR.
- On EINTR, don't count it against the retry budget, just keep retrying.
EINTR can happen in bursts.
- Log the errno on failure, and don't conditionalize that logging on
BH_ENABLE_TRACE_MMAP. In other parts of the code, error logging is not
conditional on that define, while turning on that tracing define makes
things overly verbose.