Demote a warning to debug message, if C compiler is not there (#44182)

lib/spack/spack/solver/asp.py

@@ -314,6 +314,10 @@ def using_libc_compatibility() -> bool:
     return spack.platforms.host().name == "linux"
 
 
+def c_compiler_runs(compiler: spack.compiler.Compiler) -> bool:
+    return compiler.compiler_verbose_output is not None
+
+
 def extend_flag_list(flag_list, new_flags):
     """Extend a list of flags, preserving order and precedence.
 
@@ -2975,6 +2979,13 @@ class CompilerParser:
     def __init__(self, configuration) -> None:
         self.compilers: Set[KnownCompiler] = set()
         for c in all_compilers_in_config(configuration):
+            if using_libc_compatibility() and not c_compiler_runs(c):
+                tty.debug(
+                    f"the C compiler {c.cc} does not exist, or does not run correctly."
+                    f" The compiler {c.spec} will not be used during concretization."
+                )
+                continue
+
             if using_libc_compatibility() and not c.default_libc:
                 warnings.warn(
                     f"cannot detect libc from {c.spec}. The compiler will not be used "

lib/spack/spack/test/conftest.py

@@ -2053,3 +2053,11 @@ def _true(x):
 @pytest.fixture()
 def do_not_check_runtimes_on_reuse(monkeypatch):
     monkeypatch.setattr(spack.solver.asp, "_has_runtime_dependencies", _true)
+
+
+@pytest.fixture(autouse=True, scope="session")
+def _c_compiler_always_exists():
+    fn = spack.solver.asp.c_compiler_runs
+    spack.solver.asp.c_compiler_runs = _true
+    yield
+    spack.solver.asp.c_compiler_runs = fn