Revert "Replace memcpy with the cortex-strings implementation"

This reverts commit d49c4871bbe02577ac00b367104d76370ce3d21b.
Revert "Import memchr implementation from cortex-strings for Cortex A15"

This reverts commit 003ceda8672c12667ad2ec323df094a2433b3d8e.
Revert "Replace Cortex A15 strlen implementation with cortex-strings"

This reverts commit 91d4f97bb2dc38b69b24b2b80f311161c793494a.
Merge musl's alignment optimized strlen with some changes.
Merge musl's alignment optimized strlen with some changes.