Up to now, Spack was allowing all build-tools that
may appear in the DAG to have 2 max_dupes.
This is not needed in practice for most of them,
and adding them out of caution just increases
grounding and concretization time.
This PR makes the value of max_dupes configurable
per package, and sets only a few known packages to
2 max_dupes by default.
In case user needs different values, they can
tune the configuration for their use case.
ccd205bfeb