MFi386 r253328:
Create a proper stack frame for amd64 version of bcopy().  Note that
this also makes the stack properly aligned in the function, despite it
is not strictly needed.

Sponsored by:	The FreeBSD Foundation
MFC after:	1 week


git-svn-id: svn+ssh://svn.freebsd.org/base/head@274279 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f