gccrs: Initial implementation of v0 mangling

gcc/rust/ChangeLog:

	* backend/rust-compile-context.h:
	* backend/rust-mangle.cc (struct V0Path): New struct.
	(v0_path): New function.
	(legacy_mangle_name):
	(v0_numeric_prefix):
	(v0_complex_type_prefix):
	(v0_add_integer_62): Deleted
	(v0_integer_62): New function.
	(v0_add_opt_integer_62): Deleted.
	(v0_opt_integer_62): New function.
	(v0_add_disambiguator): Deleted.
	(v0_disambiguator): New function.
	(v0_type_prefix): Support more types.
	(v0_generic_args): New function.
	(v0_add_identifier): Deleted.
	(v0_identifier): New function.
	(v0_type_path): New function.
	(v0_function_path): New function.
	(v0_scope_path): New function.
	(v0_crate_path): New function.
	(v0_inherent_or_trait_impl_path): New function.
	(v0_mangle_item): Use v0_path.
	(Mangler::mangle_item):
	* backend/rust-mangle.h (class Context):
	* hir/tree/rust-hir-item.h:

Signed-off-by: Raiki Tamura <[email protected]>

gcc/rust/backend/rust-compile-context.h

@@ -340,9 +340,9 @@ class Context
   bool const_context_p (void) { return (const_context > 0); }
 
   std::string mangle_item (const TyTy::BaseType *ty,
-			   const Resolver::CanonicalPath &path) const
+			   const Resolver::CanonicalPath &path)
   {
-    return mangler.mangle_item (ty, path);
+    return mangler.mangle_item (this, ty, path);
   }
 
   void push_closure_context (HirId id);