MIDL2008
The documentation lists this name without a value.
Documented in Win32
sparse enums require /c_ext or /ms_ext Assigning values to enumeration constants is not compatible with DCE RPC. If you want to use the Microsoft extensions to MIDL that permit assigning values to enumeration constants,you cannot compile with the /osf switch, which enforces strict DCE compatibility. MIDL versions 3.0 and later use the /c_ext and /ms_ext switches as the default; the /osf switch turns off these extension switches.