Information about an include directive in a SourceFile.
If the include directive required a macro expansion to get the filename,
the is_macro will return true. If the include directive was actually an
include_next, then is_next will return true.
Attributes Summary:
The target SourceFile object being referenced.
The name by which the target is referenced.
True if the directive uses a macro.
True if this is using #include_next (GNU extension).