offlineAudioContext exposes 32-bit archs

While doing QA on i686 I found that Linux and Windows have a different offlineAudioContext on TZP compared to x86_64.

It's 24fc63ce for me (both on Windows and on Linux, but both are VMs on my amd64 host. On Linux I tested on 32-bit OS, on Windows I tested on 64-bit OS) vs. a7c1fbb6. I have on Windows+Linux x86_64.