compiler-tests-suite cannot check negative answers for self-defined var_test

[rundong08]

Description

Even after applying the workaround in #20, compiler-tests-suite still cannot check for negative answers (or in fact any answer not in the range 0-255). For example,
Let's say we have a var_test_5.rkt file with simple content

(- 1)

and when you run racket run-tests.rkt, it will generate error like

--------------------
var_test_5 > compiler tests > code generation
FAILURE
name:       check
location:   utilities.rkt:2275:46
params:     '(#<procedure:result-check> 255 "-1")
message:    "Mismatched output from x86 execution"
--------------------

Expected Behavior (assuming your compiler implementation is correct)

All tests should pass

Cause

compiler-tests-suite uses exit code to check result. However, on most system, exit code will be truncated to the lowest 8-bit (0-255), such that -1 became 255.

Workaround

Modify your self-defined var_test to return a nonnegative number.