CRuntime_Musl: More fixes for time64

[omerfirmak]

The original PR (#3275) missed quite a few spots and conversions,
which led to the build on Alpine Linux failing with Aithmetic Exception
on core.time module constructor.
Links to the two offending commits are included.
For further issues / investigation, search for 'time64' in the git repository.

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Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "stable + druntime#3384"

[RazvanN7]

What is the relationship between this PR and #3384 ? It seems that some changes are overlapping. Why not make a single PR with multiple commits?

[kinke]

This targets stable, #3383 dmd-cxx (presumably for bootstrapping).

[RazvanN7]

@kinke Ok to merge this?