SDL_assert: add support for aarch64-w64-mingw32
GCC 15 development branch provides an experimental support for Windows on ARM64, which will be officially released next year, according to latest news.
I tried to compile SDL2 with this new compiler but I got a tiny problem into SDL_assert.h because it couldn't find the right platform.
However, it has been easy to fix and I included it into this PR.
More details can be also found here:
https://learn.microsoft.com/en-us/cpp/intrinsics/debugbreak?view=msvc-170
(cherry picked from commit 2cb1a2d0a7f1c9cb3177c907758322899c3041d5)