tests: add sync.test

* tests/sync.c: New file.
* tests/sync.test: New test.
* tests/.gitignore: Add sync.
* tests/Makefile.am (check_PROGRAMS): Likewise.
(DECODER_TESTS): Add sync.test.
diff --git a/tests/sync.test b/tests/sync.test
new file mode 100755
index 0000000..f6bf6c8
--- /dev/null
+++ b/tests/sync.test
@@ -0,0 +1,6 @@
+#!/bin/sh
+
+# Check sync syscall decoding.
+
+. "${srcdir=.}/init.sh"
+run_strace_match_diff -a7