Word-at-a-time memcpy/memmove/memset/strlen/strcmp implementing the
level-1 string slice. memcpy carries an optimize(no-tree-loop-
distribute-patterns) attribute: GCC's loop-distribution pass rewrites
its word-copy loop into a self-recursive memcpy@plt call at -O2/-O3
otherwise.
Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)
Co-authored-by: Sisyphus <[email protected]>
