debug/111080 - avoid outputting debug info for unused restrict qualified type

The following applies some maintainance with respect to type qualifiers
and kinds added by later DWARF standards to prune_unused_types_walk.
The particular case in the bug is not handling (thus marking required)
all restrict qualified type DIEs.  I've found more DW_TAG_*_type that
are unhandled, looked up the DWARF docs and added them as well based
on common sense.

	PR debug/111080
	* dwarf2out.cc (prune_unused_types_walk): Handle
	DW_TAG_restrict_type, DW_TAG_shared_type, DW_TAG_atomic_type,
	DW_TAG_immutable_type, DW_TAG_coarray_type, DW_TAG_unspecified_type
	and DW_TAG_dynamic_type as to only output them when referenced.

	* gcc.dg/debug/dwarf2/pr111080.c: New testcase.