Add link SQE support

Just a basic test case that does various forms of linked nops, and
a sample bare bones copy program using linked reads and writes.

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

examples/Makefile

@@ -1,10 +1,10 @@
 CFLAGS ?= -g -O2 -Wall -D_GNU_SOURCE -L../src/
 
-all_targets += io_uring-test io_uring-cp
+all_targets += io_uring-test io_uring-cp link-cp
 
 all: $(all_targets)
 
-test_srcs := io_uring-test.c io_uring-cp.c
+test_srcs := io_uring-test.c io_uring-cp.c link-cp.c
 
 test_objs := $(patsubst %.c,%.ol,$(test_srcs))
 
@@ -12,6 +12,8 @@ io_uring-test: io_uring-test.c
 	$(CC) $(CFLAGS) -o $@ io_uring-test.c -luring
 io_uring-cp: io_uring-cp.c
 	$(CC) $(CFLAGS) -o $@ io_uring-cp.c -luring
+link-cp: link-cp.c
+	$(CC) $(CFLAGS) -o $@ link-cp.c -luring
 
 clean:
 	rm -f $(all_targets) $(test_objs)