Propagate the SystemExit code as the process exit code

This doesn't handle all the cases that CPython does.

src/jit.cpp

@@ -154,8 +154,11 @@ int main(int argc, char** argv) {
             main_module = createAndRunModule("__main__", fn);
         } catch (ExcInfo e) {
             if (e.matches(SystemExit)) {
-                printf("Warning: ignoring SystemExit code\n");
-                return 1;
+                Box* code = e.value->getattr("code");
+                int rtncode = 1;
+                if (code && isSubclass(code->cls, pyston::int_cls))
+                    rtncode = static_cast<BoxedInt*>(code)->n;
+                return rtncode;
             } else {
                 e.printExcAndTraceback();
                 return 1;
@@ -221,8 +224,11 @@ int main(int argc, char** argv) {
                     compileAndRunModule(m, main_module);
                 } catch (ExcInfo e) {
                     if (e.matches(SystemExit)) {
-                        printf("Warning: ignoring SystemExit code\n");
-                        return 1;
+                        Box* code = e.value->getattr("code");
+                        int rtncode = 1;
+                        if (code && isSubclass(code->cls, pyston::int_cls))
+                            rtncode = static_cast<BoxedInt*>(code)->n;
+                        return rtncode;
                     } else {
                         e.printExcAndTraceback();
                     }

src/runtime/builtin_modules/sys.cpp

@@ -55,10 +55,12 @@ Box* sysExcClear() {
 }
 
 static Box* sysExit(Box* arg) {
-    if (arg)
-        raiseExc(exceptionNew1(SystemExit));
-    else
-        raiseExc(exceptionNew2(SystemExit, arg));
+    assert(arg);
+    Box* exc = exceptionNew2(SystemExit, arg);
+    // TODO this should be handled by the SystemExit constructor
+    exc->giveAttr("code", arg);
+
+    raiseExc(exc);
 }
 
 BoxedDict* getSysModulesDict() {

test/tests/sys_exit.py

+# no-collect-stats
+
+import sys
+sys.exit(0)