Remove spack.target from code (#46503)

The `spack.target.Target` class is a weird entity, that is just needed to:

1. Sort microarchitectures in lists deterministically
2. Being able to use microarchitectures in hashed containers

This PR removes it, and uses `archspec.cpu.Microarchitecture` directly. To sort lists, we use a proper `key=` when needed. Being able to use `Microarchitecture` objects in sets is achieved by updating the external `archspec`.

Signed-off-by: Massimiliano Culpo <massimiliano.culpo@gmail.com>

lib/spack/external/__init__.py

@@ -18,7 +18,7 @@
 
 * Homepage: https://pypi.python.org/pypi/archspec
 * Usage: Labeling, comparison and detection of microarchitectures
-* Version: 0.2.5-dev (commit cbb1fd5eb397a70d466e5160b393b87b0dbcc78f)
+* Version: 0.2.5-dev (commit bceb39528ac49dd0c876b2e9bf3e7482e9c2be4a)
 
 astunparse
 ----------------

lib/spack/external/archspec/cpu/microarchitecture.py

@@ -115,6 +115,9 @@ def __eq__(self, other):
             and self.cpu_part == other.cpu_part
         )
 
+    def __hash__(self):
+        return hash(self.name)
+
     @coerce_target_names
     def __ne__(self, other):
         return not self == other