[BUGFIX] fix typo in build_lib.sh

[lgg]

there is no such variable as $make_config, changed to $cmake_config

[mxnet-bot]

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[lgg]

@lanking520 hello. What you mean by pr-work-in-progress?

It's just a typo in additional script output, it only needed for user debug and doesn't affect on other parts of script or entire project.