Introduce prototype-style function definition for POWER memmove.

Upstream removed the old-style definition in:

commit d6f68bbef4427850c2901728a1d13efc0e687297

Author: Adhemerval Zanella <azanella@linux.vnet.ibm.com>

Date:   Tue Jun 24 06:42:31 2014 -0500

    PowerPC: memmove default implementation cleanup

diff --git a/sysdeps/powerpc/memmove.c b/sysdeps/powerpc/memmove.c

index 50734e45458352c5..7d736bc0b0eb7d63 100644

--- a/sysdeps/powerpc/memmove.c

+++ b/sysdeps/powerpc/memmove.c

@@ -40,10 +40,7 @@

 #endif

 rettype

-MEMMOVE (a1, a2, len)

-     a1const void *a1;

-     a2const void *a2;

-     size_t len;

+MEMMOVE (a1const void *a1, a2const void *a2, size_t len)

 {

   unsigned long int dstp = (long int) dest;

   unsigned long int srcp = (long int) src;