Compiler macro with no function handled suboptimally

[Bike]

cleavir-env does not have any provision for the client to indicate that a compiler macro definition (or ftype proclamation, or whatever) has been seen but no function definition has been seen. Cleavir only signals a condition if there is no information at all, i.e. function-info returns nil. Cleavir should probably be able to detect this situation and issue a warning or error for the client, with a continue restart that just applies the compiler macro.