Dumb change to support x86_64-nacl

This is definitely not enough or simply wrong, but works in most cases.
From the debug stub point of view, this should behave as expected in most cases as well.

BUG=http://code.google.com/p/nativeclient/issues/detail?id=2896
TEST=

Review URL: https://chromiumcodereview.appspot.com/10700182
1 file changed