Instead of trying a homegrown way to avoid recursive exceptions, let's do it with the defined procedure C++ has for this case: call std::terminate.
This allowed removing some old hackery inherited from Boom and will now hopefully allow sanitizing the exit procedure to the point that it can be done without depending on exit handlers.
GCC: this use of "defined" may not be portable [-Wexpansion-to-defined]
Clang: macro expansion producing 'defined' has undefined behavior [-Wexpansion-to-defined]
This reverts commit b8c0e78c91 et al.
Instead, use the already provided access function I_FindName to get the file name from findstate_t.
Also made the contents of findstate_t private so that use of the access functions is required to retrieve the information and direct access triggers a compile error.
This fixes two issues:
* timer related texture animations are not being recreated multiple times if a scene renders multiple viewpoints (e.g. camera textures or portals.)
* interpolation is smoother when maps have a high think time of multiple milliseconds. A good map to see the difference would be ZDCMP2 which has a think time of 4-5 milliseconds. With the timer taken in real time after the thinkers have run and VSync on this resulted in alternating time slices of 11 and 21 ms between frame interpolations instead of an even 16 as should be done for smooth 60 fps because roughly every second frame was offset by those 5 ms.
Most of those which still rely on ZDoom's own definition should be gone, unfortunately the code in files that include Windows headers is a gigantic mess with DWORDs being longs there intead of ints, so this needs to be done with care. DWORD should only remain where the Windows type is actually wanted.
The only reason this even existed was that ZDoom's original VC projects used __fastcall. The CMake generated project do not, they stick to __cdecl.
Since no performance gain can be seen by using __fastcall the best course of action is to just remove all traces of it from the source and forget that it ever existed.
