document fake handles

Author: beepster4096

src/shims/windows/foreign_items.rs

@@ -330,6 +330,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                 // We just make this the identity function, so we know later in `NtWriteFile` which
                 // one it is. This is very fake, but libtest needs it so we cannot make it a
                 // std-only shim.
+                // FIXME: this should return real HANDLEs when io support is added
                 this.write_scalar(Scalar::from_machine_isize(which.into(), this), dest)?;
             }
             "CloseHandle" => {
@@ -372,6 +373,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
             "GetProcessHeap" if this.frame_in_std() => {
                 let [] = this.check_shim(abi, Abi::System { unwind: false }, link_name, args)?;
                 // Just fake a HANDLE
+                // It's fine to not use the Handle type here because its a stub
                 this.write_scalar(Scalar::from_machine_isize(1, this), dest)?;
             }
             "GetModuleHandleA" if this.frame_in_std() => {