Remove the old concretizer (#45215)

The old concretizer is still used to bootstrap clingo from source. If we switch to a DAG model
where compilers are treated as nodes, we need to either:

1. fix the old concretizer to support this (which is a lot of work and possibly research), or
2. bootstrap `clingo` without the old concretizer.

This PR takes the second approach and gets rid of the old concretizer code. To bootstrap
`clingo`, we store some concrete spec prototypes as JSON, select one according to the
coarse-grained system architecture, and tweak them according to the current host.

The old concretizer and related dead code are removed.  In particular, this removes
`Spec.normalize()` and related methods, which were used in many unit-tests to set
up the test context. The tests have been updated not to use `normalize()`.

- [x] Bootstrap clingo concretization based on a JSON file
- [x] Bootstrap clingo *before* patchelf
- [x] Remove any use of the old concretizer, including:
      * Remove only_clingo and only_original fixtures
      * Remove _old_concretize and _new_concretize
      * Remove _concretize_together_old
      * Remove _concretize_together_new
      * Remove any use of `SPACK_TEST_SOLVER`
      * Simplify CI jobs
- [x] ensure bootstrapping `clingo` works on on Darwin and Windows
- [x] Raise an intelligible error when a compiler is missing
- [x] Ensure bootstrapping works on FreeBSD
- [x] remove normalize and related methods

Signed-off-by: Todd Gamblin <tgamblin@llnl.gov>

etc/spack/defaults/config.yaml

@@ -170,23 +170,6 @@ config:
   # If set to true, Spack will use ccache to cache C compiles.
   ccache: false
 
-
-  # The concretization algorithm to use in Spack. Options are:
-  #
-  #   'clingo': Uses a logic solver under the hood to solve DAGs with full
-  #       backtracking and optimization for user preferences. Spack will
-  #       try to bootstrap the logic solver, if not already available.
-  #
-  #   'original': Spack's original greedy, fixed-point concretizer. This
-  #       algorithm can make decisions too early and will not backtrack
-  #       sufficiently for many specs. This will soon be deprecated in
-  #       favor of clingo.
-  #
-  # See `concretizer.yaml` for more settings you can fine-tune when
-  # using clingo.
-  concretizer: clingo
-
-
   # How long to wait to lock the Spack installation database. This lock is used
   # when Spack needs to manage its own package metadata and all operations are
   # expected to complete within the default time limit. The timeout should

etc/spack/defaults/windows/config.yaml

@@ -1,6 +1,5 @@
 config:
   locks: false
-  concretizer: clingo
   build_stage::
     - '$spack/.staging'
   stage_name: '{name}-{version}-{hash:7}'