Set CONDA_OVERRIDE_ARCHSPEC for Linux x86_64
This MR fixes #72 (closed) by specifying CONDA_OVERRIDE_ARCHSPEC
for the Linux x86_64 builds to haswell
which forces the solver to choose packages built with instruction sets that are compatible with Microarchitecture level 3 CPUs.
This should mean that the IGWN environments are compatible with the widest array of architectures, at the cost of some performance hits on newer systems that could leverage advanced instructions.
Edited by Duncan Macleod