Just a tiny bugfix I spotted: The `f(un)lockfile` wrappers in
`format-inl.h` that wrap Windows's `_(un)lock_file` methods are
defined with a trailing return type derived by using decltype on a
hypothetical call to the underlying functions.
The wrappers don't contain a `return` in their bodies, however, so if
the return type of the underlying functions were to ever change from
`void`, there would be a compile error. This just adds `return` to each.
be98ea8add