Ease `IMUL 5, h1` 32 bits hash (~10 % for > 256 B).
Ease `IMUL 5, h1` 32 bits hash (~10 % for > 256 B).

Replace by a left shift and an addition. Generated code for 64 bits
version already map to the even most adequate `LEA`.

On a mid-2012 MBA,

benchmark                    old MB/s     new MB/s     speedup
Benchmark32_1-4              90.18        91.08        1.01x
Benchmark32_2-4              168.26       168.55       1.00x
Benchmark32_4-4              342.13       338.26       0.99x
Benchmark32_8-4              587.46       584.68       1.00x
Benchmark32_16-4             981.80       990.72       1.01x
Benchmark32_32-4             1349.67      1370.62      1.02x
Benchmark32_64-4             1684.94      1696.83      1.01x
Benchmark32_128-4            1748.24      1746.80      1.00x
Benchmark32_256-4            1805.96      1933.24      1.07x
Benchmark32_512-4            1845.56      2019.75      1.09x
Benchmark32_1024-4           1856.36      2031.61      1.09x
Benchmark32_2048-4           1890.43      2032.47      1.08x
Benchmark32_4096-4           1881.13      2085.36      1.11x
Benchmark32_8192-4           1889.83      2103.02      1.11x

spaolacci/murmur3