gcc: fix crash on non-void func. without return

make it workable with aggresive optimization flags

src/burn/zet.cpp

@@ -512,17 +512,17 @@ int ZetPc(int n)
 
 int ZetBc(int n)
 {
-
+    return 0;
 }
 
 int ZetDe(int n)
 {
-
+    return 0;
 }
 
 int ZetHL(int n)
 {
-
+    return 0;
 }
 
 int ZetScan(int nAction)
@@ -571,7 +571,7 @@ int ZetNmi()
 int ZetIdle(int nCycles)
 {
     Drz80.nCyclesTotal += nCycles;
-
+    return 0;
 }
 
 int ZetSegmentCycles()

src/sdl-dingux/sdl_progress.cpp

@@ -94,6 +94,7 @@ int ProgressCreate()
 	//DrawString("Based on FinalBurnAlpha", (uint16 *)load_screen->pixels, 10, 35, fwidth);
 	DrawString("Now loading ...", (uint16 *)load_screen->pixels, 10, 105, fwidth);
 	show_rom_loading_text("Reading ROM", 0, 0);
+	return 0;
 }
 
 int ProgressDestroy()
@@ -102,6 +103,7 @@ int ProgressDestroy()
 		SDL_FreeSurface(load_screen);
 		load_screen = NULL;
 	}
+	return 0;
 }
 
 int ProgressUpdateBurner(double dProgress, const TCHAR* pszText, bool bAbs)

src/sdl-dingux/state.cpp

@@ -43,6 +43,7 @@ static int StateInfo(int* pnLen, int* pnMinVer, int bAll)
 static int __cdecl ReadAcb(struct BurnArea* pba)
 {
 	fread(pba->Data, 1, pba->nLen, bfp);
+	return 0;
 }
 
 // State load
@@ -198,6 +199,7 @@ static int __cdecl WriteAcb(struct BurnArea *pba)
 	//printf("WRITE ACB - len: %i, name: %s\n", pba->nLen, pba->szName);
 	fwrite(pba->Data, 1, pba->nLen, bfp);
 	nTotalLen += pba->nLen;
+	return 0;
 }
 
 // Write a savestate as a chunk of an "FBS " file