Stub enough Struct changes to load specs

Author: chrisseaton

spec/tags/core/struct/new_tags.txt

@@ -1,3 +1,8 @@
 fails:Struct.new overwrites previously defined constants with string as first argument
 fails:Struct.new raises a ArgumentError if passed a Hash with an unknown key
 fails:Struct.new keyword_init: false option behaves like it does without :keyword_init option
+fails:Struct.new keyword_init: true option creates a class that accepts keyword arguments to initialize
+fails:Struct.new keyword_init: true option new class instantiation accepts arguments as hash as well
+fails:Struct.new keyword_init: true option new class instantiation raises ArgumentError when passed not declared keyword argument
+fails:Struct.new keyword_init: true option new class instantiation raises ArgumentError when passed a list of arguments
+fails:Struct.new keyword_init: true option new class instantiation raises ArgumentError when passed a single non-hash argument

spec/truffle.mspec

@@ -58,7 +58,6 @@ class MSpecScript
   set :core, [
     "spec/ruby/core",
 
-    "^spec/ruby/core/struct/new_spec.rb",
     "^spec/ruby/core/tracepoint",
     "^spec/ruby/core/dir/glob_spec.rb",
     "^spec/ruby/core/dir/element_reference_spec.rb"

src/main/ruby/core/struct.rb

@@ -33,7 +33,7 @@ class << self
     alias_method :subclass_new, :new
   end
 
-  def self.new(klass_name, *attrs, &block)
+  def self.new(klass_name, *attrs, keyword_init: true, &block)
     if klass_name
       if klass_name.kind_of? Symbol # Truffle: added to avoid exception and match MRI
         attrs.unshift klass_name