Revert "Added optimization by Lee Killough"

This early commit causes crashes on maps E4M3, E4M9 and Plutonia MAP12 (#34)

I'm pretty sure this issue due to a buggy memmove function on OpenWatcom, but will look onto it.

FASTDOOM/r_bsp.c

@@ -104,10 +104,13 @@ void R_ClipSolidWallSegment(int first,
             next = newend;
             newend++;
 
-            // 1/11/98 killough: performance tuning using fast memmove
-            memmove(start + 1, start, (++newend - start) * sizeof(*start));
-            start->first = first;
-            start->last = last;
+            while (next != start)
+            {
+                *next = *(next - 1);
+                next--;
+            }
+            next->first = first;
+            next->last = last;
             return;
         }