start to add some SOUND_TRIGGER_ACHIEVEMENTS code

Start to add supporting code to windsound and macsound. The latter
remains commented out because I haven't had a chance to try
it on macOS yet.

In order to test it out, I added two more stock sounds:
sa2_xplevelup and sa2_xpleveldown.

src/allmain.c

@@ -626,8 +626,12 @@ init_sound_and_display_gamewindows(void)
 
     activate_chosen_soundlib();
 
-    SoundAchievement(0, sa2_splashscreen, 0);
-    /* ToDo: new splash screen invocation will go here */
+    if (iflags.wc_splash_screen && !flags.randomall) {
+        SoundAchievement(0, sa2_splashscreen, 0);
+        /* ToDo: new splash screen invocation will go here */
+    } else {
+        SoundAchievement(0, sa2_newgame_nosplash, 0);
+    }
 
     WIN_MESSAGE = create_nhwindow(NHW_MESSAGE);
     if (VIA_WINDOWPORT()) {