Recently, kdeedu gained a dependency on math/kig, which brings in some
heavyweight dependencies:

devel/boost-python-libs
devel/libunwind
math/blas
math/cblas
math/lapack
math/metis
math/openblas
math/py-numpy
math/suitesparse

This is particularly painful on powerpc64, where openblas does not even
build (yet).

This patch turns on option KIG on x86 only.

The impact on arm is TBD.

PR: 238721
Approved by: tcberner