test: setup PYTHONIOENCODING on Windows

This is required to ensure that we encode the strings correctly when
redirected.  This allows the printing to succeed where it would fail
previously due to encoding failures.

Author: compnerd

test/lit.cfg

@@ -183,6 +183,9 @@ def append_to_env_path(directory):
     config.environment['PATH'] = \
         os.path.pathsep.join((directory, config.environment['PATH']))
 
+if kIsWindows:
+    config.environment['PYTHONIOENCODING'] = 'UTF8'
+
 # Tweak the PATH to include the tools dir and the scripts dir.
 if swift_obj_root is not None:
     llvm_tools_dir = getattr(config, 'llvm_tools_dir', None)