tar failed when generate capi package

[tensor-tang]

When I use paddle/scripts/docker/build.sh to generate c-api package, it crashed at tar.

+ cd /paddle/build/capi_output/usr/local
+ ls
+ egrep -v '^Found.*item$'
+ xargs tar /paddle/build/paddle.tgz
tar: invalid option -- '/'

This error is also encountered here.

The reason that #7237 passed the PR_CI is that WITH_C_API was disabled, so it did not actually run into function gen_capi_package.

As teamcity build log 9644 for #7237 shows:

+ gen_capi_package
[07:19:56]W: [Step 1/1] + [[ '' == \O\N ]]
[07:19:56]W: [Step 1/1] + [[ OFF == \O\N ]]
[07:19:56]W: [Step 1/1] + printf 'If you need to install PaddlePaddle in de
velop docker image,'
[07:19:56]W: [Step 1/1] + printf 'please make install or pip install build/python/dist/.whl.\n'
[07:19:56] : [Step 1/1] If you need to install PaddlePaddle in develop docker image,please make install or pip install build/python/dist/.whl.
[07:19:56] : [Step 1/1]

how to reproduce this issue:

use below script:

#!/bin/bash
set -xe
export PADDLE_DEV_NAME="paddlepaddle/paddle:latest-dev"
docker run -i --rm -v $PWD:/paddle ${PADDLE_DEV_NAME} \
  rm -rf /paddle/build
docker run  -i --rm -v $PWD:/paddle \
  -e "WITH_PYTHON=OFF" \
  -e "WITH_SWIG_PY=OFF" \
  -e "WITH_PYTHON=OFF" \
  -e "WITH_C_API=ON" \
  -e "WITH_GPU=OFF" \
  -e "WITH_AVX=ON" \
  -e "WITH_MKL=ON" \
  -e "WITH_STYLE_CHECK=OFF" \
  ${PADDLE_DEV_NAME} \
  bash -x /paddle/paddle/scripts/docker/build.sh