Suppress switch with only default warning for Windows builds

We get this case occasionally - just seen one in TableGen

Change-Id: I4ffe6345620e35ccf57172325a13cccae4738084
git-pf-unshelve: stg@2125239

llvm/cmake/modules/HandleLLVMOptions.cmake

@@ -559,6 +559,8 @@ if (MSVC)
           # v15.8.8. Re-evaluate the usefulness of this diagnostic when the bug
           # is fixed.
       -wd4709 # Suppress comma operator within array index expression
+          # Cases arise from TableGen that result in this type of switch
+      -wd4065 # Suppress: 'switch statement contains 'default' but no 'case' labels'
 
       # Ideally, we'd like this warning to be enabled, but even MSVC 2019 doesn't
       # support the 'aligned' attribute in the way that clang sources requires (for