libiberty: Add support for D `typeof(*null)' types

libiberty: Add support for D `typeof(*null)' types

The D language has a new bottom type `typeof(*null)'.  Null types were
also incorrectly being demangled as `none', this has been fixed to be
`typeof(null)'.

libiberty/ChangeLog:

	* d-demangle.c (dlang_attributes): Handle typeof(*null).
	(dlang_type): Likewise.  Demangle 'n' as typeof(null).
	* testsuite/d-demangle-expected: Update tests.