travis: Add timestamps to all build messages
travis: Add timestamps to all build messages

When debugging why builds are taking so long it's often useful to get the
timestamp of all log messages as we're not always timing every tiny step of the
build. I wrote a [utility] for prepending a relative timestamp from the start of
a process which is now downloaded to the builders and is what we wrap the entire
build invocation in.

[utility]: https://github.com/alexcrichton/stamp-rs

Closes #40577

aidancully/rust,GBGamer/rust,graydon/rust,GBGamer/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,GBGamer/rust,GBGamer/rust,graydon/rust,aidancully/rust,GBGamer/rust,graydon/rust,GBGamer/rust,GBGamer/rust,aidancully/rust,aidancully/rust,graydon/rust,GBGamer/rust