fix little C-code problems that trigger clang errors/warnings

src/racket/src/eval.c

@@ -12840,7 +12840,6 @@ static Scheme_Object *write_syntax(Scheme_Object *obj)
     case scheme_begin0_sequence_type:
       break;
     default:
-      *(long *)0x0 = 1;
       break;
     }
   }

src/racket/src/jit.c

@@ -13601,10 +13601,10 @@ static void check_stack(void)
 
     if (q == stack_cache_pop_code) {
       if (!pos)
-	*(long *)0x0 = 1;
+	abort();
       else {
 	if (stack_cache_stack[pos].stack_frame != (void *)(((void **)p) + RETURN_ADDRESS_OFFSET)) {
-	  *(long *)0X0 = 1;
+	  abort();
 	}
 	--pos;
       }

src/wxxt/utils/image/src/wx_img.cc

@@ -672,8 +672,8 @@ void wxImage::FloydDitherize1(XImage * /* ximage */)
   /* same as FloydDitherize8, but output is a 1-bit per pixel XYBitmap,
      packed 8 pixels per byte */
 
-  register short *dp;
-  register byte   pix8, bit;
+  short          *dp;
+  byte           pix8, bit;
   short          *dithpic;
   int             i, j, err, bperln, order;
   byte           *pp, *image, w, blck, w8, b8;