Build failure with clang on older CPU :Illegal instruction

[Luke Benes]

I confirmed that git bisect identified the wrong commit, probably because I didn't run a `make clean` between builds. Also confirmed that Tomaž's patch https://gerrit.libreoffice.org/#/c/82422/
allows a successful build on older CPUs.

Superb job tracking down and fixing this issue despite my bad bisect. Thanks Tomaž and Luboš!

-Luke