[C++][NIGHTLY:test-conda-cpp-valgrind] GenerateBitsUnrolled triggers valgrind on uninit inputs

[asfimport]

https://github.com/ursacomputing/crossbow/runs/1877315066#step:6:2818

Comparison kernels generate an output bitmap for all array values, including those masked by a null bit. This should be fine since the indeterminate bits are also masked in the output but valgrind still triggers on the branching in GenerateBitsUnrolled.

Reporter: Ben Kietzman / @bkietz
Assignee: Ben Kietzman / @bkietz

PRs and other links:

• GitHub Pull Request #9471

_{Note: This issue was originally created as ARROW-11595. Please see the migration documentation for further details.}

[asfimport]

Antoine Pitrou / @pitrou:
Issue resolved by pull request 9471
#9471