tests: add read-write.test

* tests/read-write.c: New file.
* tests/read-write.test: New test.
* tests/.gitignore: Add read-write.
* tests/Makefile.am (check_PROGRAMS): Likewise.
(DECODER_TESTS): Add read-write.test.
diff --git a/tests/.gitignore b/tests/.gitignore
index 3d6d93e..c240a11 100644
--- a/tests/.gitignore
+++ b/tests/.gitignore
@@ -99,6 +99,7 @@
 preadv-pwritev
 pselect6
 pwritev
+read-write
 readdir
 readlink
 readlinkat