When discussing this in the last team meeting, Andrew wasn't a huge fan of mucking with environment variables to achieve this, but left the decision to me. Adding to the PR description, I'm going to merge it because:

• Wine's default WINEDEBUG setting is fine for end users running GUI applications, but is terrible for people running Zig applications through zig build because it spams their console output with useless messages.
  • (Unless the zig build user happens to be a Wine developer who's specifically interested in actually addressing the messages, which seems highly unlikely.)
  • This is doubly bad because the red stderr warnings demonstrably mislead people into thinking that their build has failed.
• It's extremely unlikely that the Wine project would take a patch to change this established default because it's been this way for so many years (decades?), and it provides useful output for Wine developers to diagnose problems when end users run Windows GUI applications.
• There is no way to achieve the effect of WINEDEBUG=-all with command line flags that I know of (unfortunately).
• It's also unlikely that Wine would take a patch to add a command line flag; compare the rather short output of wine --help with the amount of environment variables in man wine. I think there's a clear design philosophy here.

I feel confident that this patch is the right call for most (if not all) Zig users using zig build -fwine. But we can always revert if it turns out that there's an angle I've failed to consider.