Auto merge of #96837 - tmiasko:stdio-fcntl, r=joshtriplett

Use `fcntl(fd, F_GETFD)` to detect if standard streams are open

In the previous implementation, if the standard streams were open,
but the RLIMIT_NOFILE value was below three, the poll would fail
with EINVAL:

> ERRORS: EINVAL The nfds value exceeds the RLIMIT_NOFILE value.

Switch to the existing fcntl based implementation to avoid the issue.

Fixes #96621.

Author: bors