Spec is incorrect about what is considered a COM interface

[dlangBugzillaToGithub]

ponce reported this on 2017-11-03T13:38:10Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=17963

Description

The spec says:
"A COM interface is defined as one that derives from the interface core.stdc.win­dows.com.IUnknown."
https://dlang.org/spec/interface.html#com-interfaces

However an interface derived from another interface named "IUnknown", whatever its content and fully qualified name, will also be considered COM, with the semantics restrictions.
This is very desirable since it allow to use COM interfaces with sayn @nogc signatures, or COM without Windows.

So the spec is wrong about this, core.stdc.win­dows.com.IUnknown is not needed, but the name "IUnknown" is.