tcg/i386: Implement cmp_vec with avx512 insns

tcg/i386: Implement cmp_vec with avx512 insns

The sse/avx instruction set only has EQ and GT as direct comparisons.
Other signed comparisons can be generated from swapping and inversion.
However unsigned comparisons are not available and must be transformed
to signed comparisons by biasing the inputs.

The avx512 instruction set has a complete set of comparisons, with
results placed into a predicate register.  We can produce the normal
cmp_vec result by using VPMOVM2*.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>