[FS#254] Build error with additional libustream library (check_data_file_clashes)

[LEDE Bugs]

The following task has a new comment added:

FS#254 - Build error with additional libustream library (check_data_file_clashes)
User who did this - Jo-Philipp Wich (jow-)

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You may only builtin one ustream library at a time.
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More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=254#comment894