Bug 1840931 - More properly handle files > 4GB in elfhack. r=gsvelto, a=RyanVM

I'm pretty sure there are other theoretical problems in the code,
notably when a single section is larger than 4GB, but by the time
we reach that limit, bug 1839740 will have been fixed.

Differential Revision: https://phabricator.services.mozilla.com/D182447