test/dtrace: use TracePoint.__enable

"TracePoint.enable" is implemented in prelude.rb since
r66003 / commit 96990203b7
and not available in miniruby.  I tried using regular "ruby"
for testing, but it proved noisy and caused test failures.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@66336 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/dtrace/test_function_entry.rb

@@ -77,7 +77,7 @@ ruby$target:::method-return
     private
     def ruby_program
       <<-eoruby
-      TracePoint.new{}.enable
+      TracePoint.new{}.__enable(nil, nil)
       class Foo
 	def foo; end
       end

test/dtrace/test_singleton_function.rb

@@ -46,7 +46,7 @@ ruby$target:::method-return
 
     def ruby_program
       <<-eoruby
-      TracePoint.new{}.enable
+      TracePoint.new{}.__enable(nil, nil)
       class Foo
 	def self.foo; end
       end