Fix SSE and NEON compiler autodetection for MSVC

For library users who do not set the defines to detect the ISA, we try to auto-detect from the compiler. Currently for MSVC this does not work, as we use the `__SSE2__` style defines, which MSVC does not set except for AVX2. 

This means that for some users (e.g. Godot engine) the builds are falling back to using "None" builds for both x86-64 and Arm64 Windows hosts.