[PATCH] Fix rwlock stall with PREFER_WRITER_NONRECURSIVE_NP (bug 23861)

[Florian Weimer]

* Andreas Schwab:

> +volatile int do_exit;

Please no volatile, and use the GCC __atomic builtins instead (not the
glibc-internal ones, which are inaccessible).  I think the minimum GCC
version does not yet support proper C11 atomics.

Thanks,
Florian