regress: introduce TT_RETRIABLE

We have some tests that has false-positive due to real/CPU time bound,
but they are pretty generic and we do not want to skip them by default.

TT_RETRIABLE is the flag that will indicate tinytest to retry the test
in case of failure, use it to avoid next possible false-positives:
- real time-related
- CPU time-related
Since I guess it is better to see/grepping RETRYING messages over
ignoring completely failed builds.

No configuration switch for number of retries was done on purpose (only
3 retries and no more).

And this is how it looks BTW:
  $ gcc ../test/tinytest_demo.c ../test/tinytest.c
  $ ./a.out --verbose --no-fork
  demo/timeout_retry
  demo/timeout_retry:
    FAIL ../test/tinytest_demo.c:201: assert(i != 1): 1 vs 1
    [timeout_retry FAILED]

    [RETRYING timeout_retry (3)]
  demo/timeout_retry:
           OK ../test/tinytest_demo.c:201: assert(i != 1): 2 vs 1
           OK ../test/tinytest_demo.c:213: assert(t2-t1 >= 4): 5 vs 4
           OK ../test/tinytest_demo.c:215: assert(t2-t1 <= 6): 5 vs 6
  1 tests ok.  (0 skipped)

1 files changed, 4 insertions, 1 deletions

diff --git a/test/tinytest.h b/test/tinytest.h
index ed07b26b..d321dd46 100644
--- a/test/tinytest.h
+++ b/test/tinytest.h
@@ -34,8 +34,11 @@
 #define TT_ENABLED_  (1<<2)
 /** Flag for a test that's off by default. */
 #define TT_OFF_BY_DEFAULT  (1<<3)
+/** Flag for a test that should be runned again in case of failure (but not
+ * more then 3 times). */
+#define TT_RETRIABLE	(1<<4)
 /** If you add your own flags, make them start at this point. */
-#define TT_FIRST_USER_FLAG (1<<4)
+#define TT_FIRST_USER_FLAG (1<<5)
 
 typedef void (*testcase_fn)(void *);