Debug stub: fix test_interrupt test.
Debug stub: fix test_interrupt test.

The fix ensures that program is interrupted inside test_interrupt function
where there are no syscalls.

BUG= http://code.google.com/p/nativeclient/issues/detail?id=3237
TEST= run_debug_stub_test
Review URL: https://codereview.chromium.org/11722002

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@10521 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

sbc100/native_client,sbc100/native_client,nacl-webkit/native_client,sbc100/native_client,sbc100/native_client,nacl-webkit/native_client,nacl-webkit/native_client,sbc100/native_client,sbc100/native_client,nacl-webkit/native_client,nacl-webkit/native_client