Display compiler warnings for macros with missing imports

[Vasilij Schneidermann]

The compiler already displays warnings for procedures with missing imports which is super useful, especially when compiling code that's not wrapped in a module (wrapping it in a module will turn the warnings into errors). However there is no equivalent for macros with missing imports and neither does wrapping them into a module produce a warning or error. This leads to less than obvious errors if you later import such a macro into other code and compile it, you'll then get an error for the import you forgot to add for the macro's module. See #1603 for an example.