Use unsafe blocks in assert.h implementation

src/header/assert/mod.rs

 //! assert implementation for Redox, following http://pubs.opengroup.org/onlinepubs/7908799/xsh/assert.h.html
 
+// TODO: set this for entire crate when possible
+#![deny(unsafe_op_in_unsafe_fn)]
+
 use crate::{c_str::CStr, platform::types::*};
 
 #[no_mangle]
@@ -9,9 +12,9 @@ pub unsafe extern "C" fn __assert_fail(
     line: c_int,
     cond: *const c_char,
 ) -> ! {
-    let func = CStr::from_ptr(func).to_str().unwrap();
-    let file = CStr::from_ptr(file).to_str().unwrap();
-    let cond = CStr::from_ptr(cond).to_str().unwrap();
+    let func = unsafe { CStr::from_ptr(func) }.to_str().unwrap();
+    let file = unsafe { CStr::from_ptr(file) }.to_str().unwrap();
+    let cond = unsafe { CStr::from_ptr(cond) }.to_str().unwrap();
 
     eprintln!("{}: {}:{}: Assertion `{}` failed.", func, file, line, cond);