If you were previously using this, it will no longer have any effect.
SSE2 and NEON will be used if supported, but can be disabled with
`MA_NO_SSE2` and `MA_NO_NEON`.

Maintaining AVX2 optimizations by hand is not worth the effort. The use
of AVX2 is now dependent on the compiler's auto-vectorization function.

Public issue https://github.com/mackron/miniaudio/issues/582

Public issue https://github.com/mackron/miniaudio/issues/582

Checking for __ORBIS__ and __PROSPERO__ first avoid identifying PS4/PS5 as BSD systems.

In a stereo scenario, the listener will use a channel map of
{SIDE_LEFT, SIDE_RIGHT}, but sounds will default to
{FRONT_LEFT, FRONT_RIGHT}. As a result, channel mapping will be
performed to do the conversion. By instead defaulting stereo sounds
to be consistent with the listener, a passthrough path can be used
instead, improving efficiency.