mpy-cross needs a --version option

[goatchurchprime]

It seems like it's really important when you build the mpy-cross compiler from source that it matches exactly the version of the micropython on the device.

When you log on to the device you get a detailed version of micropython on the command prompt, like so:
"MicroPython v1.9.3-8-g63826ac5c on 2017-11-01"

Is there a way to get an equally specific version code from the mpy-cross program?

In an attempt to get to the correct one, I am doing:

git tag --list
git checkout tags/v1.9.3
cd mpy-cross
make

But you can never be sure this is going to be exactly right, and this can be one fiendish source of bugs.

I can see no hidden code supporting this option already in place:
https://github.com/micropython/micropython/blob/master/mpy-cross/main.c

[peterhinch]

See #3357.

[SpotlightKid]

See also this relevant forum discussion: https://forum.micropython.org/viewtopic.php?p=23524#p23524
A --version option would indeed be very helpful and should also include the Bytecode version produced by the particular mpy-cross binary.

[dpgeorge]

See #4739 for a patch to do this.

[dpgeorge]

Option added in 7e90e22