All mkmf tests pass except test_have_library

Author: eregon

test/mri/failing.exclude

@@ -125,17 +125,7 @@ minitest/test_minitest_mock.rb
 minitest/test_minitest_spec.rb
 minitest/test_minitest_unit.rb
 misc/test_ruby_mode.rb
-mkmf/test_config.rb
-mkmf/test_constant.rb
-mkmf/test_convertible.rb
-mkmf/test_find_executable.rb
-mkmf/test_flags.rb
-mkmf/test_framework.rb
-mkmf/test_have_func.rb
 mkmf/test_have_library.rb
-mkmf/test_have_macro.rb
-mkmf/test_libs.rb
-mkmf/test_signedness.rb
 net/http/test_https.rb
 net/imap/test_imap.rb
 net/imap/test_imap_response_parser.rb