MFC r340888

MFC r340888

sfxge(4): fix warnings from VS2015 C compiler (C4100)

Fix multiple level 4 warnings
"C4100: 'xxx': unreferenced formal parameter"
no functional changes.

The _NOTE(ARGUNUSED(xxx)) annotations are being exposed to the Visual
Studio 2015 C compiler with the following:

  #define _NOTE_ARGUNUSED(...) UNREFERENCED_PARAMETER((__VA_ARGS__));
  #define _NOTE(_annotation)   _NOTE_ ## _annotation

Submitted by:   Andrew Lee <alee at solarflare.com>
Sponsored by:   Solarflare Communications, Inc.
MFC after:      1 week
Differential Revision:  https://reviews.freebsd.org/D18122