table of function pointers exported via a wine private symbol?
i think this doesn't work, since some modules (e.g. in `dinput/tests` and `ntoskrnl.exe/tests`) don't link with ntdll.dll, we can't use `LdrGetDllHandle` etc. in our asan thunk.
so looks like unused slot in PEB is the way to go. IIUC at least a page is allocated for the PEB, and PEB doesn't use up the full page? we should be able to put a pointer there.