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;