itimer_thread_func doesn't handle EINTR when poll returns -1

Summary

An error (-1) return of the call to poll in itimer_thread_func added in e5383a29 unconditionally results in sysErrorBelch, even when the poll failed because of EINTR.

Normally, this can't happen, because the thread is set up with a signal mask for all blockable signals. However, in my Haskell Landlock bindings, libcap's psx library is used to ensure all threads in a process get landlocked, which relies on SIGSYS being sent to all threads in a process and having a handler in place. To make this work, the library tells the linker to wrap sigfillset with a version which ensures SIGSYS is not masked, so poll can return -1 with EINTR in errno.

Using TEMP_FAILURE_RETRY (or a local equivalent) should fix this.

Steps to reproduce

Build and run the landlock-readme test of rev a512fadb767e715d0f4f8ca59470d584775282c4 of landlock-hs.

Expected behavior

Everything works as it did before e5383a29, where a "failed" read would be checked for EINTR and handled accordingly.

Environment

• GHC version used: 9.8.2

Optional:

• Operating System: Linux
• System Architecture: x86_64