Unit test runner ergonomics

- Catch and classify as INTERNAL_ERROR unix signals thrown by
  reference model
- Made -t a required argument

Change-Id: I2be1ed6f5c1e862d6a3aee43c6b1e8575ab50d1f
Signed-off-by: Jared Smolens <jared.smolens@arm.com>
diff --git a/verif/tosa_ref_run.py b/verif/tosa_ref_run.py
index c14f490..de35d93 100644
--- a/verif/tosa_ref_run.py
+++ b/verif/tosa_ref_run.py
@@ -66,6 +66,9 @@
                     result = TosaTestRunner.Result.EXPECTED_FAILURE
                 else:
                     result = TosaTestRunner.Result.UNEXPECTED_FAILURE
+            elif rc < 0:
+                # Unix signal caught (e.g., SIGABRT, SIGSEGV, SIGFPE, etc)
+                result = TosaTestRunner.Result.INTERNAL_ERROR
             else:
                 raise Exception(f"Return code ({rc}) unknown.")