`make tidy` should run first on the buildbots

[huonw]

It seems silly to spend 20 minutes building if there is trailing whitespace or a line > 100 chars, which is only discovered at the start of make check.

[pnkfelix]

Or maybe tidy should be one of the default make targets, since it is cheap to run?

[pnkfelix]

(maybe both. huonw's point is legitimate; it would save buildbot time.)

[pnkfelix]

part of #8058 .

(I feel like I've seen evidence that this actually happened at some point recently?)

[huonw]

Triage: no change to the buildbots, but now we have have travis CI building every PR, so people get tidy feedback fast and this is essentially irrelevant.