Bug#1029568: xsimd: tests fail on armhf: Cannot access memory, store location is not properly aligned

[Drew Parsons]

Source: xsimd
Followup-For: Bug #1029568

The source of the armhf test error is actually the -mfpu=neon added
explicitly in debian/rules to DEB_CXXFLAGS_MAINT_APPEND on armhf.

Remove this flag, then armhf tests pass.

As far as other arches go, in general they should pass tests now (running
scalar tests).  I checked that tests pass on ppc64 and mipsel, for
instance.

powerpc failed because it does not have "-march=native".
https://github.com/xtensor-stack/xsimd/pull/296/files fixed that for
ppc64, but replacing the "ppc64" reference in tests/CMakeLists.txt
with "ppc*" simply results in 0 tests running on powerpc (so no point
testing it).