Fix issue #269

Patch from here
http://lists.nongnu.org/archive/html/qemu-devel/2015-11/msg03848.html

Also fix another potential issue with constants from
bbeb82395e (diff-9e0011b4d4a5890b309421630e6d86c3)

qemu/tcg/tcg.c

@@ -2053,6 +2053,7 @@ static void tcg_reg_alloc_mov(TCGContext *s, const TCGOpDef *def,
             ts->mem_coherent = 1;
         } else if (ts->val_type == TEMP_VAL_CONST) {
             tcg_out_movi(s, itype, ts->reg, ts->val);
+            ts->mem_coherent = 0;
         }
         s->reg_to_temp[ts->reg] = args[1];
         ts->val_type = TEMP_VAL_REG;