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>

.github/workflows/unit_tests.yaml

@@ -16,38 +16,27 @@ jobs:
       matrix:
         os: [ubuntu-latest]
         python-version: ['3.7', '3.8', '3.9', '3.10', '3.11', '3.12']
-        concretizer: ['clingo']
         on_develop:
         - ${{ github.ref == 'refs/heads/develop' }}
         include:
-        - python-version: '3.11'
-          os: ubuntu-latest
-          concretizer: original
-          on_develop: ${{ github.ref == 'refs/heads/develop' }}
         - python-version: '3.6'
           os: ubuntu-20.04
-          concretizer: clingo
           on_develop: ${{ github.ref == 'refs/heads/develop' }}
         exclude:
         - python-version: '3.7'
           os: ubuntu-latest
-          concretizer: 'clingo'
           on_develop: false
         - python-version: '3.8'
           os: ubuntu-latest
-          concretizer: 'clingo'
           on_develop: false
         - python-version: '3.9'
           os: ubuntu-latest
-          concretizer: 'clingo'
           on_develop: false
         - python-version: '3.10'
           os: ubuntu-latest
-          concretizer: 'clingo'
           on_develop: false
         - python-version: '3.11'
           os: ubuntu-latest
-          concretizer: 'clingo'
           on_develop: false
 
     steps:
@@ -85,7 +74,6 @@ jobs:
     - name: Run unit tests
       env:
           SPACK_PYTHON: python
-          SPACK_TEST_SOLVER: ${{ matrix.concretizer }}
           SPACK_TEST_PARALLEL: 2
           COVERAGE: true
           UNIT_TEST_COVERAGE: ${{ matrix.python-version == '3.11' }}
@@ -182,7 +170,6 @@ jobs:
     - name: Run unit tests (full suite with coverage)
       env:
           COVERAGE: true
-          SPACK_TEST_SOLVER: clingo
       run: |
           share/spack/qa/run-unit-tests
     - uses: codecov/codecov-action@e28ff129e5465c2c0dcc6f003fc735cb6ae0c673
@@ -213,7 +200,6 @@ jobs:
         brew install dash fish gcc gnupg2 kcov
     - name: Run unit tests
       env:
-        SPACK_TEST_SOLVER: clingo
         SPACK_TEST_PARALLEL: 4
       run: |
         git --version