A protocol composition with an explicit 'AnyObject' member is
now mangled as <protocol list> 'Xl'. For subclass existentials,
I changed the mangling from <protocol list> <class> 'XE' to
<protocol list> <class> 'Xl'.
Not used for anything just yet.
Previously it was part of swiftBasic.
The demangler library does not depend on llvm (except some header-only utilities like StringRef). Putting it into its own library makes sure that no llvm stuff will be linked into clients which use the demangler library.
This change also contains other refactoring, like moving demangler code into different files. This makes it easier to remove the old demangler from the runtime library when we switch to the new symbol mangling.
Also in this commit: remove some unused API functions from the demangler Context.
fixes rdar://problem/30503344
