sys: Fix CFComparatorFunction and move it to `base` module
CFComparatorFunction declaration was missing one argument (void *context).
Here's its declaration from CFBase.h:
```c
typedef CFComparisonResult (*CFComparatorFunction)(const void *val1, const void *val2, void *context);
```
And its declaration in array.rs:
```rust
pub type CFComparatorFunction = extern "C" fn(val1: *const c_void, val2: *const c_void) -> CFComparisonResult;
```
Since it's declared in CFBase.h, I moved it to `base` module.
bors-servo
9236908e07