Environment variables control the disabling of certain explicit SIMD optimizations.
x64 options:
TH_NO_AVX2=1 # disable AVX2 codepaths
TH_NO_AVX=1 # disable AVX codepaths
TH_NO_SSE=1 # disable SSE codepaths
ppc64le options:
TH_NO_VSX=1 # disable VSX codepaths