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/core/os2/SDL_os2.h

@@ -0,0 +1,31 @@
+#ifndef _SDL_os2_h
+#define _SDL_os2_h
+
+#include "SDL_log.h"
+#include "SDL_stdinc.h"
+#include ".\src\core\os2\geniconv\geniconv.h"
+
+#if OS2DEBUG==SDLOUTPUT
+
+# define debug(s,...) SDL_LogDebug( SDL_LOG_CATEGORY_APPLICATION, \
+                                    __func__"(): "##s, ##__VA_ARGS__ )
+
+#elif defined(OS2DEBUG)
+
+# define debug(s,...) printf( __func__"(): "##s"\n", ##__VA_ARGS__ )
+
+#else
+
+# define debug(s,...)
+
+#endif // OS2DEBUG
+
+
+// StrUTF8New() - geniconv\sys2utf8.c.
+#define OS2_SysToUTF8(S) StrUTF8New( 1, S, SDL_strlen( S ) + 1 )
+#define OS2_UTF8ToSys(S) StrUTF8New( 0, (char *)(S), SDL_strlen( S ) + 1 )
+
+// SDL_OS2Quit() will be called from SDL_QuitSubSystem().
+void SDL_OS2Quit();
+
+#endif // _SDL_os2_h