Use ptr::cast instead of as casts in several places. (#3507)

`ptr::cast` has the advantage of being unable to silently cast
`*const T` to `*mut T`. This turned up several places that were
performing such casts, which this PR also fixes.

crates/jit/src/code_memory.rs

@@ -200,11 +200,7 @@ unsafe fn register_unwind_info(obj: &File, text: &[u8]) -> Result<Option<UnwindR
         return Ok(None);
     }
     Ok(Some(
-        UnwindRegistration::new(
-            text.as_ptr() as *mut _,
-            unwind_info.as_ptr() as *mut _,
-            unwind_info.len(),
-        )
-        .context("failed to create unwind info registration")?,
+        UnwindRegistration::new(text.as_ptr(), unwind_info.as_ptr(), unwind_info.len())
+            .context("failed to create unwind info registration")?,
     ))
 }