Add static SIMD support to XXH3 in core:hash/xxhash.

This uses compile-time features to decide how large of a SIMD vector to
use. It currently has checks for amd64/i386 to size its vectors for
SSE2/AVX2/AVX512 as necessary.

The generalized SIMD functions could also be useful for multiversioning
of the hash procs, to allow for run-time dispatch based on available CPU
features.

core/hash/xxhash/xxhash_3_other.odin

@@ -0,0 +1,8 @@
+#+build !amd64
+#+build !i386
+package xxhash
+
+import "base:runtime"
+
+XXH_NATIVE_WIDTH :: min(XXH_MAX_WIDTH,
+	2 when runtime.HAS_HARDWARE_SIMD else 1)