gpgscm: Limit the number of parallel jobs.

* ffi.c (do_wait_processes): Suppress the timeout error.
* tests.scm (semaphore): New definition.
(test-pool): Only run a bounded number of tests in parallel.
(test::started?): New function.
(run-tests-parallel): Do not report results, do not start the tests.
(run-tests-sequential): Adapt.
(run-tests): Parse the number of parallel jobs.
--

This change limits the number of tests that are run in parallel.  This
way we do not overwhelm the operating systems' scheduler.  As a
side-effect, we also get more accurate runtime information, and it
will be easy to implement timeouts on top of this.

Use TESTFLAGS to limit the number of jobs:

    $ make check-all TESTFLAGS=--parallel=16

Signed-off-by: Justus Winter <justus@g10code.com>

tests/gpgscm/ffi.c

@@ -915,6 +915,8 @@ do_wait_processes (scheme *sc, pointer args)
                               retcodes);
   if (err == GPG_ERR_GENERAL)
     err = 0;	/* Let the return codes speak.  */
+  if (err == GPG_ERR_TIMEOUT)
+    err = 0;	/* We may have got some results.  */
 
   for (i = 0; i < count; i++)
     retcodes_list =