[PATCH, AArch64]: Further strcpy improvements. Add stpcpy.

[Richard Earnshaw <rearnsha at arm dot com>]

This patch is a further performance improvement for short strings using
strcpy.  The main changes are to eliminate further conditional branches
that are hard to predict and to apply some simplifications that fall out
of those changes.  Furthermore, we are now more likely to fall-through
conditional branches on the likely path, which helps branch prediction
further.

The patch also adds the ability to use the same code to build stpcpy.

Committed.

Attachment: newlib-strcpy.patch
Description: Text document