gh-152548: Skip test_eintr where fcntl is unavailable

test_eintr.py was renamed from the never-collected _test_eintr.py, so its
top-level "import fcntl" now runs on every platform and crashed the module
import on Windows and WASI.  Import fcntl through import_helper so the whole
module is skipped there instead, as the EINTR tests only run on Unix.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: serhiy-storchaka

Lib/test/test_eintr.py

@@ -10,7 +10,6 @@
 
 import contextlib
 import faulthandler
-import fcntl
 import os
 import platform
 import select
@@ -23,10 +22,15 @@
 import unittest
 
 from test import support
+from test.support import import_helper
 from test.support import isolation
 from test.support import os_helper
 from test.support import socket_helper
 
+# This module is collected on every platform, but the EINTR tests only run on
+# Unix; skip the whole module where fcntl (and thus the rest) is unavailable.
+fcntl = import_helper.import_module('fcntl')
+
 
 # gh-109592: Tolerate a difference of 20 ms when comparing timings
 # (clock resolution)