test: add a lit configuration for Windows subdirectory

This adds a local configuration to the Windows subdirectory to filter
out the tests on non-Windows platforms using the lit filtering.

GitOrigin-RevId: 6488bd1d51715501632778e3c9a1d4eedfac2998
diff --git a/test/Shell/Process/Windows/lit.local.cfg b/test/Shell/Process/Windows/lit.local.cfg
new file mode 100644
index 0000000..c10f33b
--- /dev/null
+++ b/test/Shell/Process/Windows/lit.local.cfg
@@ -0,0 +1,2 @@
+if 'system-windows' not in config.available_features:
+  config.unsupported = True