util/bitset: Return an actual bool from test macros

I want to be able to do BITSET_TEST() != BITSET_TEST() and this isn't
currently possible because BITSET_TEST() returns a random bit.  Compare
to zero to get an actual Boolean.

Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
14 jobs for !773 with review/bitset-test-return-bool in 8 minutes and 1 second (queued for 1 second)
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passed debian #274777

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  Build+Test
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