Here's the patch we use when building SDL-1.2.14 and 1.2-hg on Haiku,

it only affects Haiku specific files so should be ok to apply in hg.

-Scott McCreary
HaikuPorts

src/main/beos/SDL_BeApp.cc

@@ -39,13 +39,15 @@ static SDL_Thread *SDL_AppThread = NULL;
 
 static int StartBeApp(void *unused)
 {
+  if(!be_app) {
 	BApplication *App;
 
 	App = new BApplication("application/x-SDL-executable");
 
 	App->Run();
 	delete App;
-	return(0);
+  }
+ return(0);
 }
 
 /* Initialize the Be Application, if it's not already started */
@@ -86,7 +88,7 @@ int SDL_InitBeApp(void)
 	++SDL_BeAppActive;
 
 	/* The app is running, and we're ready to go */
-	return(0);
+ return(0);
 }
 
 /* Quit the Be Application, if there's nothing left to do */

src/video/bwindow/SDL_sysvideo.cc

@@ -57,7 +57,6 @@ static void BE_UnlockHWSurface(_THIS, SDL_Surface *surface);
 static void BE_FreeHWSurface(_THIS, SDL_Surface *surface);
 
 static int BE_ToggleFullScreen(_THIS, int fullscreen);
-static SDL_Overlay *BE_CreateYUVOverlay(_THIS, int width, int height, Uint32 format, SDL_Surface *display);
 
 /* OpenGL functions */
 #if SDL_VIDEO_OPENGL

src/video/bwindow/SDL_sysyuv.h

@@ -62,7 +62,7 @@ struct private_yuvhwdata
 };
 
 extern BBitmap * BE_GetOverlayBitmap(BRect bounds, color_space cs);
-SDL_Overlay* BE_CreateYUVOverlay(_THIS, int width, int height, Uint32 format, SDL_Surface* display);
+extern SDL_Overlay* BE_CreateYUVOverlay(_THIS, int width, int height, Uint32 format, SDL_Surface* display);
 extern int BE_LockYUVOverlay(_THIS, SDL_Overlay* overlay);
 extern void BE_UnlockYUVOverlay(_THIS, SDL_Overlay* overlay);
 extern int BE_DisplayYUVOverlay(_THIS, SDL_Overlay* overlay, SDL_Rect* src, SDL_Rect* dst);