Patch to add mempcpy and stpcpy to libiberty

[DJ Delorie]

> This patch adds two new functions, mempcpy and stpcpy to libiberty.
> Given the sizes of the function bodies, (one and two lines
> respectively) I wasn't sure whether they were copyrightable.  If they
> are, let me know and I'll use the LGPL.  (My disclaimer for LIBIBERTY
> is in place if that's an issue.)

A two-line change might not be, but a wholly new file would be.  It
certainly wouldn't hurt to add it.

> Ok for mainline?

Could you please add doc fragments too, and update the .texi files?
You'll have to configure with --enable-maintainer-mode, then just
"make" should do it.