Improve generic stpcpy performance

[Richard Earnshaw <rearnsha at arm dot com>]

I noticed while going through some benchmark results that the generic
stpcpy was substantially slower than the simple_stpcpy in the benchmark
itself.

So, similar to Wilko's recent strcpy patch, this patch uses the same
approach for stpcpy.

Note that it does not help to use mempcpy, since that returns a value
that points beyond the end of the copied data.

OK?

	* string/stpcpy.c (__stpcpy): Rewrite using strlen and memcpy.

Attachment: stpcpy.patch
Description: Text document