crazy linker: Alter search for zip EOCD start

When loading directly from APK, begin searching backwards
for the zip EOCD record signature at size of EOCD record
bytes before the end of the file.

BUG=537205
R=rmcilroy@chromium.org

Review URL: https://codereview.chromium.org/1390553002 .

Cr-Commit-Position: refs/heads/master@{#352577}