update build system and support unix-like systems

[lndpj]

• support unix-like systems
• update build system with platform optimizations
• fetch SDL2 only if not found
• comment out cachedir support
• replace *_s with platform independent equivalents
• replace Vector3 with optionally aligned OpenMP supporting vec<N,T> with .x() accessors

Now it compiles and runs on UNIX-like systems. Please check if it still works with _MSC_VER

-- The CXX compiler identification is Clang 22.1.8
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/lib/llvm/22/bin/clang++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Found PkgConfig: /usr/bin/pkg-config (found version "2.5.1")
-- OS: Linux-x86_64 => Linux-x86_64
-- CXX: Clang/GNU
-- Build type: ReleaseStrip
-- Using IPO/LTO.
-- Found OpenGL: /usr/lib64/libOpenGL.so
-- Found ALSA: /usr/lib64/libasound.so (found version "1.2.16.1")
-- Configuring done (0.5s)
-- Generating done (0.0s)
-- Build files have been written to: /usr/src/engine/id/id2/quake/Quake.cpp

[VinceMack]

I had some linker issues with SDL2 from the CMake changes, along with a few other build errors. I don't have a unix environment setup at the moment and didn't plan on worrying about cross platform builds until I started implementing SDL3, so I'll take your word for it on the unix end. Feel free to verify the changes do not break unix support, and I'll merge the PR. @lndpj

Fix MSVC build: remove endian.h, /Gv flag, and fix SDL2 linking

• Remove Linux-only <endian.h> include from network.cpp
• Remove /Gv (vectorcall) flag that broke SDL audio callbacks
• Fix link_libraries(PRIVATE) misinterpreted as library name
• Use proper target_link_libraries with SDL2::SDL2 + SDL2::SDL2main

[illwieckz]

Don't merge this, @lndpj has no idea what he is doing, this is randomly generated AI garbage.

Merging 1000 lines of AI hallucinated code posted by someone who doesn't even know what the code does is a massive threat.

• update CMake build DaemonEngine/Daemon#1994 (comment)

[VinceMack]

Yeah, I thought the age of the account and the number of changes being made looked weird. I didn't do a deep dive into the profile, but definitely seems like some type of automated AI changes.