Merged r4717:4718 from branches/SDL-1.2: minor OS/2 DECLSPEC/SDLCALL fixes.

I reworked this a little. The 1.2 branch isn't really very elegant about this.

--HG--
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/trunk%404369

include/begin_code.h

@@ -52,6 +52,12 @@
 #  else
 #   define DECLSPEC	__declspec(dllexport)
 #  endif
+# elif defined(__OS2__)
+#   ifdef BUILD_SDL
+#    define DECLSPEC    __declspec(dllexport)
+#   else
+#    define DECLSPEC
+#   endif
 # else
 #  if defined(__GNUC__) && __GNUC__ >= 4
 #   define DECLSPEC	__attribute__ ((visibility("default")))
@@ -63,11 +69,18 @@
 
 /* By default SDL uses the C calling convention */
 #ifndef SDLCALL
-#if defined(__WIN32__) && !defined(__GNUC__)
-#define SDLCALL __cdecl
-#else
-#define SDLCALL
-#endif
+# if defined(__WIN32__) && !defined(__GNUC__)
+#  define SDLCALL __cdecl
+# elif defined(__OS2__)
+   /* Use the _System calling convention to be compatible with every OS/2
+      compiler. (Please note that this used to be _cdecl for GCC, but that
+      was a bug. Someone should go examine and fix the XFree86 integration
+      instead. We shouldn't be passing SDLCALL function pointers between SDL
+      and XFree86!) */
+#  define SDLCALL _System
+# else
+#  define SDLCALL
+# endif
 #endif /* SDLCALL */
 
 /* Removed DECLSPEC on Symbian OS because SDL cannot be a DLL in EPOC */