Fix arch conditionals in validation_cache_test.cc to follow NaCl style
Fix arch conditionals in validation_cache_test.cc to follow NaCl style

This will have the minor effect of enabling a couple of test cases on
Windows, where __i386__ and __x86_64__ are not #defined.

BUG=none
TEST=trybots

Review URL: https://codereview.chromium.org/1312013004

sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client