make check(s) pre-release problems

[Karl Berry]

With Zack's latest Python fixes, I was hoping to move towards an
Automake release, but I find myself stymied by apparently random and
unreproducible test failures. I haven't exhausted every conceivable
avenue yet, but I thought I would write in hopes that others (Zack, past
Automake developers, anyone else ...) could give it a try, and/or have
some insights.

For me, running a parallel make check (with or without parallelizing the
"internal" makes), or make distcheck, fails some tests, e.g., nodef,
nodef2, testsuite-summary-reference-log. The exact tests that fail
changes from run to run. Running the tests on their own succeeds. Ok, so
it's something in the parallelism. But why? And how to debug?

Nothing has changed in the tests. Nothing has changed in the automake
infrastructure. Everything worked for me a few weeks ago. Furthermore,
Jim ran make check with much more parallelism than my machine can
muster, and everything succeeded for him. That was with:
  make check TESTSUITEFLAGS=-j20

So what the heck?

Perhaps easier to debug: there are two targets to be run before making a
release, check-no-trailing-backslash-in-recipes and check-cc-no-c-o,
to try to ensure no reversion wrt these features. A special shell and
compiler are configured, respectively (shell scripts that check the
behavior).

These always worked before. But now, Jim gets hundreds of failures with
the first (didn't have time to try the second). I get a couple, with
both, instead of hundreds. Again the failing tests vary. In this case,
they fail for me even without parallelism.

So what the heck x 2?

Any ideas, directions, fixes, greatly appreciated. --thanks, karl.