dynapi: Deal with failure cases better, other fixes.

Fixes Bugzilla #4803.

src/SDL_assert.c

@@ -120,32 +120,14 @@ static void SDL_GenerateAssertionReport(void)
 }
 
 
+/* This is not declared in any header, although it is shared between some
+    parts of SDL, because we don't want anything calling it without an
+    extremely good reason. */
 #if defined(__WATCOMC__)
-static void SDL_ExitProcess (int);
+void SDL_ExitProcess(const int exitcode);
 #pragma aux SDL_ExitProcess aborts;
 #endif
-static SDL_NORETURN void SDL_ExitProcess(int exitcode)
-{
-#ifdef __WIN32__
-    /* "if you do not know the state of all threads in your process, it is
-       better to call TerminateProcess than ExitProcess"
-       https://msdn.microsoft.com/en-us/library/windows/desktop/ms682658(v=vs.85).aspx */
-    TerminateProcess(GetCurrentProcess(), exitcode);
-    /* MingW doesn't have TerminateProcess marked as noreturn, so add an
-       ExitProcess here that will never be reached but make MingW happy. */
-    ExitProcess(exitcode);
-#elif defined(__EMSCRIPTEN__)
-    emscripten_cancel_main_loop();  /* this should "kill" the app. */
-    emscripten_force_exit(exitcode);  /* this should "kill" the app. */
-    exit(exitcode);
-#elif defined(__HAIKU__)  /* Haiku has _Exit, but it's not marked noreturn. */
-    _exit(exitcode);
-#elif defined(HAVE__EXIT) /* Upper case _Exit() */
-    _Exit(exitcode);
-#else
-    _exit(exitcode);
-#endif
-}
+SDL_NORETURN void SDL_ExitProcess(const int exitcode);
 
 
 #if defined(__WATCOMC__)