util: Update tinyformat to upstream

Last update was in 2017.
Updates tinyformat to upstream commit 705e3f4e1de922069bf715746d35bd2364b1f98f.
Re-apply bitcoin core specific changes.

No changes that affect our use, as far as I can see, but this gets rid
of the gcc `-Wimplicit-fallthrough` warnings, at least.

Author: laanwj