rustc --version reported date is confusing

[brson]

I've heard several people express concern that their nightly was not up to date because the date reported by rustc --version is old. This date is the commit date, not the build date.

[brson]

On this subject @eddyb said

22:31 < eddyb_> brson: would be nice if it gave build info and source (git) info
22:31 < eddyb_> but clearly distinguished from each-other

to which @blaenk responded

22:35 < blaenk> yeah that'd be cool

[brson]

Easy to implement. Just need to decide what to change.

[huonw]

FWIW, even the (start of) build date may be confusing, since the nightly builds take many hours.

[brson]

Should update how rustdoc and cargo report their version at the same time.

[iKevinY]

Looks like this can be closed since #22201 has been rolled up.