Add softfp support to armhf builders

We want to end up with one auto builder configuration. This will use Precise, which is armhf by default, but we still want to test the softfp Cortex-A8+VFP and soft float ARMv5 configurations.

Precise supports armhf and armel on the same filesystem. Add support so the config properly goes through for building GCC and the benchmarks. May need Matthias's multiarch support.