Introduce prototype-style function definition for 32-bit POWER wcsrchr.
Upstream removed the old-style function definition in:

commit bb04e529f60df7138a4fe5f1ed016dd87ade59a3
Author: Adhemerval Zanella <azanella@linux.vnet.ibm.com>
Date:   Mon Oct 14 09:26:07 2013 -0500

    PowerPC: multiarch wcsrchr for PowerPC32

diff --git a/sysdeps/powerpc/powerpc32/power6/wcsrchr.c b/sysdeps/powerpc/powerpc32/power6/wcsrchr.c
index 333650190afff171..4deb44966915679f 100644
--- a/sysdeps/powerpc/powerpc32/power6/wcsrchr.c
+++ b/sysdeps/powerpc/powerpc32/power6/wcsrchr.c
@@ -21,9 +21,7 @@
 
 /* Find the last occurrence of WC in WCS.  */
 wchar_t *
-wcsrchr (wcs, wc)
-     const wchar_t *wcs;
-     const wchar_t wc;
+wcsrchr (const wchar_t *wcs, const wchar_t wc)
 {
   const wchar_t *wcs2 = wcs + 1;
   const wchar_t *retval = NULL;