Add os.eventfd, os.eventfd_read and os.eventfd_write to Linux for Python 3.10+ (#10768)

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>

stdlib/posix.pyi

@@ -236,6 +236,16 @@ if sys.platform != "win32":
             removexattr as removexattr,
             setxattr as setxattr,
         )
+
+        if sys.version_info >= (3, 10):
+            from os import (
+                EFD_CLOEXEC as EFD_CLOEXEC,
+                EFD_NONBLOCK as EFD_NONBLOCK,
+                EFD_SEMAPHORE as EFD_SEMAPHORE,
+                eventfd as eventfd,
+                eventfd_read as eventfd_read,
+                eventfd_write as eventfd_write,
+            )
     else:
         from os import chflags as chflags, lchflags as lchflags, lchmod as lchmod
 
@@ -330,6 +340,7 @@ if sys.platform != "win32":
             CLONE_SYSVSEM as CLONE_SYSVSEM,
             CLONE_THREAD as CLONE_THREAD,
             CLONE_VM as CLONE_VM,
+            unshare as unshare,
         )
 
     # Not same as os.environ or os.environb