WIP: codegen: add B-ASIC commit hash in VHDL preamble

This adds the (short) Git commit ID of HEAD to the VHDL codegen preamble. Useful when debugging generated code.

Ex:

--
-- This code was automatically generated by the B-ASIC toolbox.
-- Code generation timestamp: (2023-03-15 14:47:44.405842)
-- B-ASIC short commit hash: fa55492
-- URL: https://gitlab.liu.se/da/B-ASIC
--

library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;

changed the description

I just realized that this does not work when your working directory is outside of the B-ASIC git project. Might need some tweaking here. Anyway, it's worth investigating how to to this properly since such a feature would be good to have.

changed title from codegen: add B-ASIC commit hash in VHDL preamble to WIP: codegen: add B-ASIC commit hash in VHDL preamble

Is this still needed or did it get in through another MR?

I would say that a feature like this would be really good for the code generation stuff. I believe this particular commit snuck in elsewhere, as I needed it to keep track of source code versions for FPL. I'll see if I can make a better version of this later today or this weekend, as I think it is important. In the meantime, I would say to leave this PR be.