Fix test_platform on cygwin. When running from build area, sys.executable is 'python'. But 'python' is actually a directory, 'python.exe' is the executable.
Fix test_platform on cygwin. When running from build area, sys.executable
is 'python'. But 'python' is actually a directory, 'python.exe' is the
executable.

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator