Update FATE reference due to WAVE channel mask now being set correctly.

This removes warnings about strict aliasing violations.
Signed-off-by: Mans Rullgard <mans@mansr.com>

The third argument of OP_U8_ALTIVEC is evaluated at most once so
there is no need for a potentially unused temporary variable.
Signed-off-by: Mans Rullgard <mans@mansr.com>

This flag is no longer used.
Signed-off-by: Mans Rullgard <mans@mansr.com>

An assembler able to cope with AVX instructions is now required.

All modern assemblers have this capability.  Older NASM versions
that lack the capability produce code that crashes at runtime,
so it's better to error out during the build process instead.

CC: libav-stable@libav.org