x/build: missing failure output from windows-amd64-2008 builder

[bcmills]

https://build.golang.org/log/59a049ac56f1c7dbcf9de1f6002512a70f765e0c is marked as a failure on the dashboard, but its output doesn't contain the word FAIL anywhere.

It's not obvious to me whether the test timed out, or failed without output. Better output from cmd/dist and/or the Builder infrastructure would probably help.

(CC @andybons @cagedmantis @toothrot @dmitshur)

[dmitshur]

This is very strange.