io_uring: add a few test tools

This adds two test programs in tools/io_uring/ that demonstrate both
the raw io_uring API (and all features) through a small benchmark
app, io_uring-bench, and the liburing exposed API in a simplified
cp(1) implementation through io_uring-cp.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

tools/io_uring/barrier.h

@@ -0,0 +1,16 @@
+#ifndef LIBURING_BARRIER_H
+#define LIBURING_BARRIER_H
+
+#if defined(__x86_64) || defined(__i386__)
+#define read_barrier()	__asm__ __volatile__("":::"memory")
+#define write_barrier()	__asm__ __volatile__("":::"memory")
+#else
+/*
+ * Add arch appropriate definitions. Be safe and use full barriers for
+ * archs we don't have support for.
+ */
+#define read_barrier()	__sync_synchronize()
+#define write_barrier()	__sync_synchronize()
+#endif
+
+#endif