Assembly optimization of strncpy for PowerPC64, using double words instead of bytes to copy strings.
Performance gain with different string size:
| **String size (bytes)** | **size <= 8** | **16 <= size <= 32** | **64 <= size <= 128** | **256 <= size <= 512** | **1024 <= size <= 2048**
| Gain rate | -0,12 | 2,43 | 9,45 | 29,13 | 59,93