Generalize config checks tests

This is mainly about the checks that are automatically generated by
`generate_config_checks.py`, but we can also use it to assert manually
written tests.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

Author: gilles-peskine-arm

scripts/mbedtls_framework/test_config_checks_generator.py renamed to scripts/mbedtls_framework/unittest_config_checks.py

@@ -1,4 +1,8 @@
-"""Test the configuration checks generated by generate_config_checks.py.
+"""Test the configuration checks that reject some bad compile-time configs.
+
+This tests the output of ``generate_config_checks.py``.
+This can also let us verify what we enforce in the manually written
+checks in ``<PROJECT>_check_config.h``.
 """
 
 ## Copyright The Mbed TLS Contributors
@@ -12,7 +16,11 @@
 
 
 class TestConfigChecks(unittest.TestCase):
-    """Unit tests for checks generated by config_checks_generator."""
+    """Unit tests for checks performed via ``<PROJECT>_config.c``.
+
+    This can test the code generated by `config_checks_generator`,
+    as well as manually written checks in `check_config.h`.
+    """
 
     # Set this to the path to the source file containing the config checks.
     PROJECT_CONFIG_C = None #type: Optional[str]