widl: Fix the writing of expressions in un-typedef'd structures by using write_type_l...

widl: Fix the writing of expressions in un-typedef'd structures by using write_type_left to write out the type, which adds the "struct ..." if necessary.

Also improve the type comparison code to not crash on unnamed
structures (although further changes need to be made to fix the output
in this case) and make it more efficient by first doing a comparison
on the values of the type pointers.