Warning for a switch statement with 'default' but no 'case labels.
This warning is triggered in the ANGLE CQ and blocking a sws roll.

Bug: angleproject:4299
Change-Id: Id8d98c124e19b6a6834beb9a643b182e2d5876e7
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/40248Tested-by: Jonah Ryan-Davis <jonahr@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>