https://bugs.winehq.org/show_bug.cgi?id=54263
--- Comment #4 from Liviu Ionescu ilg@livius.net ---
despite _UCRT not being defined?
Where should this be defined?
The mingw-w64 10.0 in the toolchain is configured to use UCRT, not MSVCRT.
But the mingw-w64 9.0 in the toolchain that builds fine was also configured with UCRT, so the difference must be more subtle.