Added to check MJIT constant for the Ruby 2.3-2.5.

This commit picked from 2c13beca2c

  Co-authored-by: Colby Swandale <me@colby.fyi>

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@67214 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/webrick/test_httpserver.rb

@@ -253,7 +253,7 @@ class TestWEBrickHTTPServer < Test::Unit::TestCase
       server.virtual_host(WEBrick::HTTPServer.new(vhost_config))
 
       Thread.pass while server.status != :Running
-      sleep 1 if RubyVM::MJIT.enabled? # server.status behaves unexpectedly with --jit-wait
+      sleep 1 if defined?(RubyVM::MJIT) && RubyVM::MJIT.enabled? # server.status behaves unexpectedly with --jit-wait
       assert_equal(1, started, log.call)
       assert_equal(0, stopped, log.call)
       assert_equal(0, accepted, log.call)

test/webrick/test_server.rb

@@ -65,7 +65,7 @@ class TestWEBrickServer < Test::Unit::TestCase
     }
     TestWEBrick.start_server(Echo, config){|server, addr, port, log|
       true while server.status != :Running
-      sleep 1 if RubyVM::MJIT.enabled? # server.status behaves unexpectedly with --jit-wait
+      sleep 1 if defined?(RubyVM::MJIT) && RubyVM::MJIT.enabled? # server.status behaves unexpectedly with --jit-wait
       assert_equal(1, started, log.call)
       assert_equal(0, stopped, log.call)
       assert_equal(0, accepted, log.call)