Description: Fix undefined board_chaintool_type resulting in compilation error

IssueNo: https://gitee.com/openharmony/third_party_cJSON/issues/I5ODQ6
Feature or Bugfix: Bugfix
Binary Source: No
Signed-off-by: Nsuwenxiang <suwenxiang@huawei.com>

BUILD.gn

@@ -22,7 +22,7 @@ if (defined(ohos_lite)) {
     "cJSON_Utils.c",
   ]
 
-  if (board_chaintool_type == "iccarm") {
+  if (defined(board_toolchain_type) && board_toolchain_type == "iccarm") {
     cflags = [
       "--diag_suppress",
       "Pe513",