powerpc: Fix compiler warning on some syscalls

GCC 5.0 emits an warning when using sizeof on array function parameters
and powerpc internal syscall macros add a check for such cases.  More
specifically, on powerpc64 and powerpc32 sysdep.h:

  if (__builtin_classify_type (__arg3) != 5 && sizeof (__arg3) > 8) \
          __illegally_sized_syscall_arg3 (); \

And for sysdeps/unix/sysv/linux/utimensat.c build GCC emits:

error: ‘sizeof’ on array function parameter ‘tsp’ will return size of
‘const struct timespec *’

This patch uses the address of first struct member instead of the struct
itself in syscall macro.

sysdeps/unix/sysv/linux/utimensat.c

@@ -35,7 +35,8 @@ utimensat (int fd, const char *file, const struct timespec tsp[2],
       return -1;
     }
 #ifdef __NR_utimensat
-  return INLINE_SYSCALL (utimensat, 4, fd, file, tsp, flags);
+  /* Avoid implicit array coercion in syscall macros.  */
+  return INLINE_SYSCALL (utimensat, 4, fd, file, &tsp[0], flags);
 #else
   __set_errno (ENOSYS);
   return -1;