Debug Menu: add time of compilation to timestamp build

[ia]

• Please check if the PR fulfills these requirements

• The changes have been tested locally
• There are no breaking changes

• What kind of change does this PR introduce?
  Add time of compilation to timestamp build in Debug Menu.

• What is the current behavior?
  Timestamp in Debug Menu shows date of build only.

• What is the new behavior (if this is a feature change)?
  Timestamp in Debug Menu shows time of build (HHMMSS) right next to a date of build.

• Other information:
  While testing different builds with local changes only (i.e., can't rely on sha id info), I would like to have more "differential" way to distinguish prepared test builds. Considering that there are a perfect spot for time even on 96x16 screens, I hope it won't hurt. In addition, as you may know, a lot of timestamp build info for all kind of software usually contains not only date but time as well, so it's a well known common practice:

$ uname -a
Linux cs-default 6.1.58+ #1 SMP PREEMPT_DYNAMIC ** Mon Jan 29 15:19:25 UTC 2024 ** x86_64 GNU/Linux

[paulfertser]

Hello,
This is indeed a nice feature for debugging and I see you're extending the timestamp that's already there. However, that got me thinking about reproducible builds.
Can you please consider following https://reproducible-builds.org/docs/source-date-epoch/ to make it easier for those who might want to make the build fully reproducible later?

[paulfertser]

Re your example, https://elixir.bootlin.com/linux/v6.13.2/source/init/Makefile#L32