Fix small regression with -fdump-ada-spec

Fix small regression with -fdump-ada-spec

When the enumeration constants of an enumeration type are defined by
explicit values, the binding generated by -fdump-ada-spec does not use
an enumeration type on the Ada side, because the set of allowed values
in C/C++ is larger than the set of allowed values in Ada, but instead
use an integer subtype and defines a set of explicit constants, which
used to be of this subtype but were changed to the base type at some
point.  This reinstates the subtype for them.

gcc/c-family/
	* c-ada-spec.c (is_simple_enum): Minor tweaks.
	(dump_ada_enum_type): Add TYPE and PARENT parameters.  For non-simple
	enumeral types use again the type name for the enumeration constants.
	(dump_ada_node): Adjust call to dump_ada_enum_type.
	(dump_nested_type): Likewise.