graphics/krita: disable vc on non-x86 / non-arm64

In file included from /wrkdirs/usr/ports/graphics/krita/work/.build/libs/pigment/KoOptimizedCompositeOpFactoryPerArch_AVX2+FMA+BMI2.cpp:11:
In file included from /wrkdirs/usr/ports/graphics/krita/work/krita-5.0.8/libs/pigment/compositeops/KoOptimizedCompositeOpFactoryPerArch.h:11:
In file included from /wrkdirs/usr/ports/graphics/krita/work/krita-5.0.8/libs/pigment/compositeops/KoVcMultiArchBuildSupport.h:28:
In file included from /usr/local/include/Vc/Vc:30:
In file included from /usr/local/include/Vc/vector.h:35:
In file included from /usr/local/include/Vc/sse/vector.h:32:
In file included from /usr/local/include/Vc/scalar/../common/../sse/intrinsics.h:34:
In file included from /usr/lib/clang/13.0.0/include/x86intrin.h:13:
/usr/lib/clang/13.0.0/include/ia32intrin.h:200:10: error: use of undeclared identifier '__builtin_ia32_readeflags_u32'

return __builtin_ia32_readeflags_u32();
       ^