tests: add fsync.test

* tests/fsync.c: New file.
* tests/fsync.test: New test.
* tests/.gitignore: Add fsync.
* tests/Makefile.am (check_PROGRAMS): Likewise.
(DECODER_TESTS): Add fsync.test.
diff --git a/tests/.gitignore b/tests/.gitignore
index b709f49..68236a8 100644
--- a/tests/.gitignore
+++ b/tests/.gitignore
@@ -42,6 +42,7 @@
 fstat
 fstat64
 fstatat64
+fsync
 ftruncate
 ftruncate64
 getcwd