internal/bytealg: (re)adding mips64x compare implementation

internal/bytealg: (re)adding mips64x compare implementation

The original CL of mips64x compare function has been reverted due to wrong
implement for little endian.
Original CL: https://go-review.googlesource.com/c/go/+/196837

name                         old time/op    new time/op    delta
BytesCompare/1                 28.9ns ± 4%    22.1ns ± 0%    -23.60%  (p=0.000 n=9+8)
BytesCompare/2                 34.6ns ± 0%    23.1ns ± 0%    -33.25%  (p=0.000 n=8+10)
BytesCompare/4                 54.6ns ± 0%    40.8ns ± 0%    -25.27%  (p=0.000 n=8+8)
BytesCompare/8                 73.9ns ± 0%    49.1ns ± 0%    -33.56%  (p=0.000 n=8+8)
BytesCompare/16                 113ns ± 0%      24ns ± 0%    -79.20%  (p=0.000 n=9+9)
BytesCompare/32                 190ns ± 0%      26ns ± 0%    -86.53%  (p=0.000 n=10+10)
BytesCompare/64                 345ns ± 0%      44ns ± 0%    -87.19%  (p=0.000 n=10+8)
BytesCompare/128                654ns ± 0%      52ns ± 0%    -91.97%  (p=0.000 n=9+8)
BytesCompare/256               1.27µs ± 0%    0.07µs ± 0%    -94.14%  (p=0.001 n=8+9)
BytesCompare/512               2.51µs ± 0%    0.12µs ± 0%    -95.26%  (p=0.000 n=9+10)
BytesCompare/1024              4.99µs ± 0%    0.21µs ± 0%    -95.85%  (p=0.000 n=8+10)
BytesCompare/2048              9.94µs ± 0%    0.38µs ± 0%    -96.14%  (p=0.000 n=8+8)
CompareBytesEqual               105ns ± 0%      64ns ± 0%    -39.43%  (p=0.000 n=10+9)
CompareBytesToNil              34.8ns ± 1%    38.6ns ± 3%    +11.01%  (p=0.000 n=10+10)
CompareBytesEmpty              33.6ns ± 3%    36.6ns ± 0%     +8.77%  (p=0.000 n=10+8)
CompareBytesIdentical          29.7ns ± 0%    40.5ns ± 1%    +36.45%  (p=0.000 n=10+8)
CompareBytesSameLength         69.1ns ± 0%    51.8ns ± 0%    -25.04%  (p=0.000 n=10+9)
CompareBytesDifferentLength    69.8ns ± 0%    52.5ns ± 0%    -24.79%  (p=0.000 n=10+8)
CompareBytesBigUnaligned       5.15ms ± 0%    2.19ms ± 0%    -57.59%  (p=0.000 n=9+9)
CompareBytesBig                5.28ms ± 0%    0.28ms ± 0%    -94.64%  (p=0.000 n=8+8)
CompareBytesBigIdentical       29.7ns ± 0%    36.9ns ± 2%    +24.11%  (p=0.000 n=8+10)

name                         old speed      new speed      delta
CompareBytesBigUnaligned      204MB/s ± 0%   480MB/s ± 0%   +135.77%  (p=0.000 n=9+9)
CompareBytesBig               198MB/s ± 0%  3704MB/s ± 0%  +1765.97%  (p=0.000 n=8+8)
CompareBytesBigIdentical     35.3TB/s ± 0%  28.4TB/s ± 2%    -19.44%  (p=0.000 n=8+10)

Fixes #34549

Change-Id: I2ef29f13cdd4229745ac2d018bb53c76f2ff1209
Reviewed-on: https://go-review.googlesource.com/c/go/+/197557
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>