DSLX is different from Rust for match patterns (currently does equality comparison for any bound identifier)

The motivation is the following (incorrect) use of match:

```
fn f(x:bool, y:bool, z:bool) -> u32 {
match true {
x => u32:42,
y => u32:43,
z => u32:44,
_ => u32:45
}
}
```

Superficially this looks like it tests whether arguments x, y, or z are true and return a respective value. However, this construct creates a new temporary named `x` and binds true to it and returns 42.

This should raise a warning that the match temporaries `x`, `y`, and `z` are unused.