Disable SILGen/discard.swift on Windows.

The -Onone passes fail to remove struct_extract, so the CHECK
lines will fail.

Author: atrick

test/SILGen/discard.swift

@@ -1,6 +1,12 @@
 // RUN: %target-swift-emit-silgen -enable-experimental-feature MoveOnlyEnumDeinits -module-name test %s | %FileCheck %s --enable-var-scope
 // RUN: %target-swift-emit-sil -enable-experimental-feature MoveOnlyEnumDeinits -module-name test -sil-verify-all %s | %FileCheck %s --check-prefix CHECK-SIL --enable-var-scope
 
+// UNSUPPORTED: OS=windows-msvc
+//
+// On Windows, the struct_extract instructions are not fully cleaned up:
+// CHECK-SIL-NOT: struct_extract
+// It likely has to do with the lazy property.
+
 func invokedDeinit() {}
 
 @_moveOnly enum MaybeFile {