> And to re-iterate my point from another thread on setenv, no, "just don't call setenv() after creating threads" is not a solution

Yes it is.

> the moment you link against any 3rd-party library, you program can have arbitrarily many threads before it even reaches main().

So don't call setenv after you load any libraries. If that means you can't call setenv at all for your linking setup then so be it.