assert: Use TerminateProcess() on Windows, vs ExitProcess (thanks, Jack!).

"What I have done is use TerminateProcess rather than ExitProcess.
ExitProcess will cause Microsoft's leak detection to continue, TerminateProcess
won't. It is also technically wrong to use ExitProcess in the case of aborting
the application.

Jack Powell
Twitter @jack9267"

src/SDL_assert.c

@@ -123,7 +123,11 @@ static void SDL_GenerateAssertionReport(void)
 static SDL_NORETURN void SDL_ExitProcess(int exitcode)
 {
 #ifdef __WIN32__
-    ExitProcess(exitcode);
+    /* "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);
+
 #elif defined(__EMSCRIPTEN__)
     emscripten_cancel_main_loop();  /* this should "kill" the app. */
     emscripten_force_exit(exitcode);  /* this should "kill" the app. */