os2: add port files for SDL2-2.0.4 from Andrey Vasilkin

only geniconv/iconv.h (was from LGPL libiconv) is replaced with a generic
minimal iconv.h based on public knowledge.

src/audio/os2/SDL_os2audio.h

@@ -0,0 +1,53 @@
+/*
+  Simple DirectMedia Layer
+  Copyright (C) 1997-2016 Sam Lantinga <slouken@libsdl.org>
+
+  This software is provided 'as-is', without any express or implied
+  warranty.  In no event will the authors be held liable for any damages
+  arising from the use of this software.
+
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely, subject to the following restrictions:
+
+  1. The origin of this software must not be misrepresented; you must not
+     claim that you wrote the original software. If you use this software
+     in a product, an acknowledgment in the product documentation would be
+     appreciated but is not required.
+  2. Altered source versions must be plainly marked as such, and must not be
+     misrepresented as being the original software.
+  3. This notice may not be removed or altered from any source distribution.
+*/
+#include "../../SDL_internal.h"
+
+#ifndef _SDL_os2mm_h
+#define _SDL_os2mm_h
+
+#include "../SDL_sysaudio.h"
+
+#define  INCL_OS2MM
+#define  INCL_PM
+#define  INCL_DOS
+#define  INCL_DOSERRORS
+#include <os2.h>
+#include <os2me.h>
+
+/* Hidden "this" pointer for the audio functions */
+#define _THIS   SDL_AudioDevice *this
+
+#define NUM_BUFFERS    3
+
+typedef struct SDL_PrivateAudioData
+{
+  USHORT               usDeviceId;
+  MCI_MIXSETUP_PARMS   stMCIMixSetup;
+  HEV                  hevBuf;
+  ULONG                ulNextBuf;
+  ULONG                cMixBuffers;
+  MCI_MIX_BUFFER       aMixBuffers[NUM_BUFFERS];
+//  ULONG                ulQueuedBuf;
+} SDL_PrivateAudioData, *PSDL_PrivateAudioData;
+
+#endif /* _SDL_os2mm_h */
+
+/* vi: set ts=4 sw=4 expandtab: */