The most frequent failure for our travis builds is running into the timeout
limits when building the compiler itself. Building librustc takes a very long
amount of time, often hitting the 10 minutes with no output threshold that
travis imposes on us.
This commit switches the relevant `make` step to being wrapped in the
`travis_wait` command [1]. This command will print something once a minute so as
to not time out a build.
This will hopefully enable us to have fewer flaky builds on travis!