MemArena: Use memory placeholders for fastmem on Windows to ensure nothing allocates within the fastmem space.

[AdmiralCurtiss]

This allocates and handles our fastmem address region as a placeholder on Windows. This avoids the possibility that something else allocates memory within the fastmem address region after it has been set up.

This should fix the bug (on Windows at least) where large texture packs break emulation, such as 12404 or 11994, but I cannot 100% confirm it.

• Use old logic as fallback if VirtualAlloc2/MapViewOfFile3 are unavailable (as they would be on eg. Win7).
• Make sure we load the VirtualAlloc2/MapViewOfFile3 from the correct dll. (see Windows API sets; maybe this one...?)
• Memory cleanup on shutdown.
• Error handling.
• 32bit support.

References:
Test code
Docs on VirtualAlloc2
Docs on VirtualFree
Docs on MapViewOfFile3
Docs on UnmapViewOfFileEx

[AdmiralCurtiss]

Alright, I think I'm at a point where I want some external input on this. Lemme have it.

And for reference, yes, this does appear to fix at least one variant of the large texture pack issue. Though it's hard to say exactly due to the sporadic nature of it.

[Warepire]

Perhaps something for later, it doesn't seem like many class methods with #ifdef in them share code, would it make sense to split the class into OS-specific implementations rather than having everything in the same implementation?

[AdmiralCurtiss]

Okay, I've updated this:

• The MemArena has been split up into three separate files for each OS, which is indeed way cleaner.
• The Windows MemArena now handles the splitting/joining stuff internally, so you can just map and unmap wherever without any setup (as long as those regions are free, of course).

As far as I'm concerned, this is done now, but it still needs testing on an old Windows system that does not have VirtualAlloc2 and MapViewOfFile3. A Linux and Android implementation of a similar thing would also be good, but I'd leave that to a followup PR if that's okay.

[PatrickFerry]

I've asked a few people with the issue with texture packs to use this build and every one of them has had success in resolving the issue. They were all modern windows users though.

EDIT: I'll check if this works with Windows 7

[Pokechu22]

Apart from my comments above, the first two commits look good. I don't know enough about the Windows API to say that the 3rd commit is good, but nothing seems wrong with it either.

[AdmiralCurtiss]

Appreciate it.

[JMC47]

This has been sitting for a very long time and no one else has reviewed it. Some of the most popular modern texture packs, like the Wind Waker Hytapia one. I continue to see people on the unofficial discord running into this crash, so I think it's about time that we merged it. I'll leave this for a few more hours to give people a chance, but if no one speaks up that they plan on reviewing it, I'll just merge.

Performance shouldn't be lower, and games seem to crash less.

[AdmiralCurtiss]

Much appreciated.

[AhayriSG]

ck if this works with Window

"I'll check if this works with Windows 7"

Minimum supported client | Windows 8 (https://docs.microsoft.com/en-us/windows/win32/api/memoryapi/nf-memoryapi-unmapviewoffileex)