Target granularity setting

[manodeep]

While working with spack, I found out that installing for different cpu-types (e.g., cascadelake, sapphirerapids) was not possible while the setting was generic (as currently done). With generic, the only (optimised) targets would be x86_64_v3/v4 and not the actual micro-arch. Setting this config value to microarchitectures allows us to create optimised binaries targeting each cpu type available on the HPC system (ie queues).