I'm wary of the suggested change in the upstream bug report:

-        return vec_extract(vec_vbpermq(_data, bits), 0);
+        return vec_extract(vec_vbpermq(_data, bits), 1);

It's useful to know if this fixes the problem, and I can confirm that it
does. But without knowing _why_ this fixes the issue, it isn't clear to
me that this is a correct fix, and so I did not include it. Since
otherwise that'd suggest a significant behaviour change from older gcc,
and I haven't found a relevant compiler bug report that indicates that
this is the case.

I'd appreciate someone who understands the ISA and compiler behaviour to
verify what the correct fix should be, advocate that upstream and get it
landed. Then we can cherry-pick that fix easily enough and re-enable the
ppc64el optimisation path.

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https://bugs.launchpad.net/bugs/1758118

Title:
  src/mongo/db/fts/unicode is not optimised on ppc64el

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