While testing a game with current gecko, I saw the error
wine: Call from 0x7bc4ad90 to unimplemented function msvcrt.dll._snwprintf_s, aborting
The game needed a native msvcrt, so I had installed one with winetricks, and it didn't export that function.
So it seems that new gecko is incompatible with old msvcrt, and using native msvcrt as a workaround for bugs in wine's version is going to be harder than it used to be.
Time to fix more of them msvcrt bugs, I guess... And/or find a more up to date msvcrt.dll for winetricks.