Resolve the executable path on Mac OS when sym-linked

tests/standalone/standalone.status

 # Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 # WARNING:
 # Tests using the multitest feature where failure is expected should *also* be
 # listed in tests/lib/analyzer/analyze_tests.status without the "standalone"
 # prefix.
 
 package/invalid_uri_test: Fail, OK # CompileTimeErrors intentionally
 
 issue14236_test: Pass # Do not remove this line. It serves as a marker for Issue 14516 comment #4.
 
 javascript_compatibility_errors_test/none: Fail, OK  # Not possible to exclude or annotate with '/// none:'
 
 [ $runtime == vm ]
 package/package_isolate_test: Fail # Issue 12474
 io/observatory_test: Fail
 
 [ $runtime == vm && $system == windows ]
-io/platform_executable_test/01: RuntimeError # Issue 16994
-io/platform_executable_test/02: RuntimeError # Issue 16994
-io/platform_executable_test/04: RuntimeError # Issue 16994
-io/platform_executable_test/05: RuntimeError # Issue 16994
 io/platform_executable_test/06: RuntimeError # NEEDS TRIAGE (kevmoo)

[kustermann, 2015/06/11 18:34:27]

What's wrong with 06?

[Søren Gjesse, 2015/06/12 07:24:24]

It was broken - trying to run 'dir' with an empty path on Windows (vs. ls on
Linux/Mac), however 'dir' is not an executable on Windows. Changed it to 'cmd'
and the test is working.

 
 [ $runtime == vm && $checked ]
 # These tests have type errors on purpose.
 io/process_invalid_arguments_test: Fail, OK
 io/directory_invalid_arguments_test: Fail, OK
 io/file_invalid_arguments_test: Fail, OK
 io/internet_address_invalid_arguments_test: Fail, OK
 io/socket_invalid_arguments_test: Fail, OK
 io/stdout_bad_argument_test: Fail, OK
 # These test have type errors on purpose and take very long to run in
@@ skipping 214 matching lines @@
 io/socket_upgrade_to_secure_test: Crash # Please triage this failure.
 io/stdout_stderr_terminal_test: Crash # Instance of 'TypeOperator': type check unimplemented for _Nullary.
 io/test_extension_fail_test: Crash # (switch (Platform.op...  Unhandled node
 io/test_extension_test: Crash # (switch (Platform.op...  Unhandled node
 io/test_runner_test: Crash # (switch (arguments[0...  Unhandled node
 io/uri_platform_test: Crash # Instance of 'TypeOperator': type check unimplemented for _Nullary.
 io/web_socket_test: Crash # Instance of 'TypeOperator': type check unimplemented for _Nullary.
 io/windows_file_system_links_test: Crash # Instance of 'TypeOperator': type check unimplemented for _Nullary.
 io/zlib_test: Crash # Instance of 'TypeOperator': type check unimplemented for _Nullary.
 priority_queue_stress_test: RuntimeError # Please triage this failure.