Fixed bug 3752 - minor os2 defines

Ozkan Sezer

Attached three patches, so these minor os/2 bits get registered mainstream:

1. SDL_syswm.h: add SDL_SYSWM_OS2 to SDL_SYSWM_TYPE enum
2. SDL_platform.h: recognize __EMX__ too as __OS2__
3. begin_code.h: set SDLCALL as _System for OS/2.

include/SDL_platform.h

@@ -97,7 +97,7 @@
 #undef __OPENBSD__
 #define __OPENBSD__ 1
 #endif
-#if defined(__OS2__)
+#if defined(__OS2__) || defined(__EMX__)
 #undef __OS2__
 #define __OS2__     1
 #endif

include/SDL_syswm.h

@@ -125,7 +125,8 @@ typedef enum
     SDL_SYSWM_MIR,
     SDL_SYSWM_WINRT,
     SDL_SYSWM_ANDROID,
-    SDL_SYSWM_VIVANTE
+    SDL_SYSWM_VIVANTE,
+    SDL_SYSWM_OS2
 } SDL_SYSWM_TYPE;
 
 /**

include/begin_code.h

@@ -61,6 +61,12 @@
 #  else
 #   define DECLSPEC __declspec(dllexport)
 #  endif
+# elif defined(__OS2__) && defined(__WATCOMC__)
+#   ifdef BUILD_SDL
+#    define DECLSPEC    __declspec(dllexport)
+#   else
+#    define DECLSPEC
+#   endif
 # else
 #  if defined(__GNUC__) && __GNUC__ >= 4
 #   define DECLSPEC __attribute__ ((visibility("default")))
@@ -74,6 +80,11 @@
 #ifndef SDLCALL
 #if (defined(__WIN32__) || defined(__WINRT__)) && !defined(__GNUC__)
 #define SDLCALL __cdecl
+#elif defined(__OS2__) || defined(__EMX__)
+#define SDLCALL _System
+# if defined (__GNUC__) && !defined(_System)
+#  define _System /* for old EMX/GCC compat.  */
+# endif
 #else
 #define SDLCALL
 #endif