Make Enumerator::Chain#each treat lambdas as lambda

Previously, lambdas were converted to procs because of how
rb_block_call works.  Switch to rb_funcall_with_block, which
handles procs as procs and lambdas as lambdas.

Fixes [Bug #15613]

enumerator.c

@@ -3111,12 +3111,6 @@ enum_chain_enum_size(VALUE obj, VALUE args, VALUE eobj)
     return enum_chain_size(obj);
 }
 
-static VALUE
-enum_chain_yield_block(RB_BLOCK_CALL_FUNC_ARGLIST(_, block))
-{
-    return rb_funcallv(block, id_call, argc, argv);
-}
-
 static VALUE
 enum_chain_enum_no_size(VALUE obj, VALUE args, VALUE eobj)
 {
@@ -3148,10 +3142,9 @@ enum_chain_each(int argc, VALUE *argv, VALUE obj)
     enums = objptr->enums;
     block = rb_block_proc();
 
-
     for (i = 0; i < RARRAY_LEN(enums); i++) {
         objptr->pos = i;
-        rb_block_call(RARRAY_AREF(enums, i), id_each, argc, argv, enum_chain_yield_block, block);
+        rb_funcall_with_block(RARRAY_AREF(enums, i), id_each, argc, argv, block);
     }
 
     return obj;

test/ruby/test_enumerator.rb

@@ -864,4 +864,20 @@ class TestEnumerator < Test::Unit::TestCase
       ], enum.to_a
     }
   end
+
+  def test_chain_each_lambda
+    c = Class.new do
+      include Enumerable
+      attr_reader :is_lambda
+      def each(&block)
+        return to_enum unless block
+        @is_lambda = block.lambda?
+      end
+    end
+    e = c.new
+    e.chain.each{}
+    assert_equal(false, e.is_lambda)
+    e.chain.each(&->{})
+    assert_equal(true, e.is_lambda)
+  end
 end