mongodb ppc64el FTBFS on 1:3.4.7-1ubuntu3

Here's the log:

https://launchpad.net/ubuntu/+source/mongodb/1:3.4.7-1ubuntu3

Upstream bug: https://jira.mongodb.org/browse/SERVER-33395

As far as I can determine, it is not caused by https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84033 since neither -O0 nor -mno-optimize-swaps work around the problem.

This package builds successfully against Artful, so the cause appears to be a build dependency update. The newer compiler in Bionic seems like the most likely candidate.

Changing "vec_extract(vec_vbpermq(_data, bits), 0)" to "vec_extract(vec_vbpermq(_data, bits), 1)" does work, but it isn't clear to me what caused this to break, so I'm reluctant to upload such a change without further information or more investigation.

Disabling the use of the ppc64el optimised path works around the problem. Presumably this comes with a performance regression, but this is better than the current FTBFS status.