Three small source tweaks that let the OpenGL renderer build and run
on Apple Silicon without affecting the Windows/Linux paths:
- stdafx.h: use GLM_FORCE_NEON on ARM64 instead of GLM_FORCE_AVX2.
AVX2 pulls <immintrin.h>, which clang on ARM64 rejects because
the x86 intrinsics are unimplemented.
- utilities/utilities.cpp: provide an Apple libc++ fallback for
Now() using localtime_r + strftime, since
std::chrono::current_zone() is not yet implemented there.
- audio/audio.h: prefer Khronos-style <AL/al.h> headers when they
are on the include path (brew openal-soft) and fall back to the
deprecated Apple OpenAL.framework's <OpenAL/al.h> only otherwise.
