Add HOST_PREFER_32_BIT to support 32-bit-by-default multilib build

We already support pure 32-bit and 64-bit-by-default multilib build.
With HOST_PREFER_32_BIT we can build 32-bit-by-default multilib build.
This will be lest disruptive during the period we transition to
64-bit-by-default.

Bug: 13751317
Change-Id: I0d56ce4abbe4afeaacfd70d709f6a349791c0722