v: add @VMODHASH comptime variable to store the commit sha of a V module

[ttytm]

The PR should implement the possibility to store a commit hash of a vmodule as a compile time variable. Similar to Similar to @VHASH / @VCURRENTHASH for V itself. The reason for it is that I encountered multiple scenarios where it would be useful and function calls in constants are not yet evaluated at comptime.

[spytheman]

Please do not make breaking changes, in PRs that introduce new features, like @VMODHASH .
It is much better, if you make such PRs standalone, without changes unrelated to them, then when they are merged, make other subsequent PRs, that will use the new features, or refactor code etc.

Bootstrapping can get very entangled and tricky otherwise.

[spytheman]

Note, I do agree that a @VMODHASH feature will be very useful to have, just not with introducing it in the same PR as other changes.

[spytheman]

Excellent work 🥳 !
The new @VMODHASH will be very useful for build scripts like the one in v-analyzer.

[ttytm]

Imho it's a super cool feature. It's a little hassle in other languages to implement. It's nice to have 😄