Fix tinyformat.h switch fallthrough warnings
Fix tinyformat.h switch fallthrough warnings

This cherry-picks a tinyformat commit:

https://github.com/c42f/tinyformat/commit/8a2812d8480bfb66923eea0bb5cdda79fe4f17ba

The effect should be to remove all compilation warnings about implicit
switch fallthroughs.

Updating the entire header file to the latest release at once brings in
other changes that may be more invasive for 1.14.5, and this commit
should not interfere with a further update.

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