Use EM_ASM_PTR when the return value is a pointer

- closes https://github.com/libsdl-org/SDL/issues/8241

(cherry picked from commit 953b55dd6d)

src/SDL_assert.c

@@ -251,7 +251,7 @@ static SDL_assert_state SDLCALL SDL_PromptAssertion(const SDL_assert_data *data,
         for (;;) {
             SDL_bool okay = SDL_TRUE;
             /* *INDENT-OFF* */ /* clang-format off */
-            char *buf = (char *) EM_ASM_INT({
+            char *buf = (char *) EM_ASM_PTR({
                 var str =
                     UTF8ToString($0) + '\n\n' +
                     'Abort/Retry/Ignore/AlwaysIgnore? [ariA] :';