There should be a `--disable-debug` builder for bors

[alexcrichton]

#9530 noticed that the build no longer works with --disable-debug, which I believe is a regression on my part.

It would be nice to have one of these builders (doesn't have to run tests) to sanity check that the compiler still builds with this configuration.

[alexcrichton]

cc @brson

[alexcrichton]

Closing, I don't think is too necessary any more. We haven't had any problems related to this recently and I think bors has enough builds as-is