Unit-typed class properties crash VS when debugging

I'm not 100% confident where this bug is, or if I'm misunderstanding something, but there's something odd going on, somewhere, at least.

**Repro steps**

Create a class with a unit-typed property, like so:

```fsharp
type MyClass() =
member this.MyProperty =
()
```

**Expected behavior**

I sorta kinda expect F# to follow C#s lead here, and reject this construction at compile-time, because a unit-typed property makes only a sliver of sense.

**Actual behavior**

The compiler gives me some IL where the following is the interesting bit:

```
.method public hidebysig specialname
instance void get_MyProperty () cil managed
{
// Method begins at RVA 0x205c
// Code size 1 (0x1)
.maxstack 8

IL_0000: ret
} // end of method MyClass::get_MyProperty

// Properties
.property instance class [FSharp.Core]Microsoft.FSharp.Core.Unit MyProperty()
{
.get instance void _/MyClass::get_MyProperty()
}
```

This does not play well with some tools, like the VS debugger which crashes when trying to inspect an object with this property.

I suspect the offending part might be how a property of type `instance class Unit` has a getter returning `instance void`.

**Known workarounds**

One possible "workaround" is to turn the property into a regular method. This will be a void method that all the tooling already understands.