PR20423: improve 'struct {...} being accessed instead of member' message

PR20423: improve 'struct {...} being accessed instead of member' message

Esp. for anonymous structures, this message was not very helpful.
The new message is much more complete:

semantic error: 'struct {...}' (include/linux/types.h:175) is being accessed instead of a member such as '->counter': operator '->' at <input>:1:81
        source: probe kernel.function("dput") { println( @cast($dentry->d_inode, "struct inode")->i_count) }
                                                                                                ^