+# Propagate 'LIB' through the environment.
+if 'LIB' in os.environ:
+ config.environment['LIB'] = os.environ['LIB']
+
+# Propagate LLVM_SRC_ROOT into the environment.
+config.environment['LLVM_SRC_ROOT'] = getattr(config, 'llvm_src_root', '')
+
+# Propagate PYTHON_EXECUTABLE into the environment