ARROW-8511: [Release] In verify-release-candidate.bat, exit when CMake build fails, use Unity build
ARROW-8511: [Release] In verify-release-candidate.bat, exit when CMake build fails, use Unity build

The unity build makes things faster, but it also hides the error reported in ARROW-8510. This at least allows the release verification to pass for 0.17.0

Closes #6978 from wesm/ARROW-8511

Authored-by: Wes McKinney <3be70eed0275ec2606f002bff3514252e145d204@apache.org>
Signed-off-by: Wes McKinney <3be70eed0275ec2606f002bff3514252e145d204@apache.org>

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