[phobos] auto tester now building on x86_64

[Brad Roberts]

I need to add dmd 1.x to the auto tester at some point, but it's rather low
priority, even if easy.  For now, it's all 2.x, though it doesn't really say
that anywhere other than the checkout logs.

Starting a few minutes ago, there's now a linux x86_64 build that runs once an
hour along with the rest.  It's only building right now since none of the tests
pass yet, but this ought to help avoid regressions in buildability.

Yay for progress,
Brad