Bug#974843: fenicsx-performance-tests must not use -march=native

[Adrian Bunk]

Source: fenicsx-performance-tests
Version: 0.0~git20201022.8913e0f-1
Severity: serious

-march=native is a baseline violation.

And even worse, every rebuild (e.g. security update in stable)
might change where it can run since it makes code run only on
hardware compatible with the hardware of whatever buildd
happened to build the package.

As an example, on amd64 the same package
built on an Intel CPU might not run on any AMD CPU, but
built on an AMD CPU might not run on any Intel CPU
if -march=native is used.