runtime: check for ErrWaitDelay in runBuiltTestProg

runtime: check for ErrWaitDelay in runBuiltTestProg

ErrWaitDelay is not expected to occur in this test, but if it does
it indicates a failure mode very different from the “failed to start”
catchall that we log for other non-ExitError errors.

Updates #50436.

Change-Id: I3f4d87d502f772bf471fc17303d5a6b483446f8f
Reviewed-on: https://go-review.googlesource.com/c/go/+/446876
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Bryan Mills <bcmills@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>