[C++] Build failure with GCC 7.5.0

[kou]

Describe the bug, including details regarding any error messages, version, and platform.

test-r-rstudio-r-base-4.1-opensuse153

https://dev.azure.com/ursacomputing/crossbow/_build/results?buildId=62799&view=logs&j=0da5d1d9-276d-5173-c4c4-9d4d4ed14fdb&t=3367cfe7-6aa5-5a88-c888-e6814d74f6eb&l=1098

/arrow/cpp/src/arrow/io/compressed.cc: In member function ‘arrow::Result<std::shared_ptr<arrow::Buffer> > arrow::io::CompressedInputStream::Impl::Read(int64_t)’:
/arrow/cpp/src/arrow/io/compressed.cc:408:12: error: could not convert ‘buf’ from ‘std::unique_ptr<arrow::ResizableBuffer>’ to ‘arrow::Result<std::shared_ptr<arrow::Buffer> >’
     return buf;
            ^~~

#39807 may be related.

Component(s)

C++

[mapleFU]

I'll fix this

[kou]

Issue resolved by pull request 41025
#41025