Fix Linux host checkbuilds.

Turns out that thanks to 9d59f417 we actually
build *all* the host libraries both 32- and 64-bit. Rather than fix the
libraries (or fixing things so we don't build stuff we don't need) right now,
let's just put _FILE_OFFSET_BITS and _LARGEFILE_SOURCE back.

Change-Id: I6c2d6a6919d1518f775e0d6c050e2c774994c5bd