Distinguish between
- there is no build data (for some reason?)
- there is build data, but the cargo package didn't build a proc macro dylib
- there is a proc macro dylib, but it didn't contain the proc macro we expected
- the name did not resolve to any macro (this is now an
unresolved_macro_call even for attributes)
I changed the handling of disabled attribute macro expansion to
immediately ignore the macro and report an unresolved_proc_macro,
because otherwise they would now result in loud unresolved_macro_call
errors. I hope this doesn't break anything.
Also try to improve error ranges for unresolved_macro_call / macro_error
by reusing the code for unresolved_proc_macro. It's not perfect but
probably better than before.
