check that we have found gcc locally

This was a problem on OSX, where gcc maps to clang and didn't understand the command line argument, and then no gcc was found.

tests.py

@@ -157,6 +157,8 @@ def test_install_environment(tmp_path):
         .stdout.decode("utf-8")
         .strip()
     )
+    assert len(gcc_ver) > 3, f"Couldn't find gcc {gcc_ver=}"
+
     setup_file = release_base_dir / "spack-environments/spack_setup.sh"
     with open(setup_file, "r") as f:
         lines = f.read().replace(