binfmt-util: handle ELOOP/EACCES from automount in read-only bind mounts

binfmt-util: handle ELOOP/EACCES from automount in read-only bind mounts

When /proc is bind-mounted read-only (common in mock/Koji buildroots,
containers, and other sandboxed environments), opening
/proc/sys/fs/binfmt_misc returns ELOOP if it is an automount point
that cannot be triggered in the read-only context.

Currently binfmt_mounted_and_writable() only handles ENOENT, so ELOOP
propagates as an error. This causes test-binfmt-util to fail with
SIGABRT and disable_binfmt() to log a spurious warning at shutdown.

Treat ELOOP and EACCES the same as ENOENT: binfmt_misc is not usably
available, return false.

Note: PR #37006 (merged April 2025) addressed ELOOP in the xstatfsat()
path, but the open() call in binfmt_mounted_and_writable() remained
unhandled.

Fixes #38070