If in take-over mode, exit on fatal error

In take-over mode, the "test" is the entire binary being executed as a
child process. So, we want to exit, rather than trying to `longjmp()` to
`DeepState_ReturnToRun`, which was never initialized.

src/lib/DeepState.c

@@ -65,7 +65,13 @@ void DeepState_Crash(void) {
 DEEPSTATE_NORETURN
 void DeepState_Fail(void) {
   DeepState_TestFailed = 1;
-  longjmp(DeepState_ReturnToRun, 1);
+
+  if (FLAGS_take_over) {
+    // We want to communicate the failure to a parent process, so exit.
+    exit(DeepState_TestRunFail);
+  } else {
+    longjmp(DeepState_ReturnToRun, 1);
+  }
 }
 
 /* Mark this test as passing. */