Implement Deref<Target=ByteStr> for CStr

This produces a deref chain of `CStr` -> `BStr` -> `[u8]` which is
present in the Rust-for-Linux analogues of these types.

Link: #134915
Link: Rust-for-Linux/linux#1075
Link: https://lore.kernel.org/all/20250221142816.0c015e9f@eugeo/
Link: Rust-for-Linux/linux#1146

Author: tamird

library/core/src/ffi/c_str.rs

@@ -710,6 +710,14 @@ impl AsRef<CStr> for CStr {
     }
 }
 
+impl ops::Deref for CStr {
+    type Target = crate::bstr::ByteStr;
+
+    fn deref(&self) -> &Self::Target {
+        crate::bstr::ByteStr::from_bytes(self.to_bytes())
+    }
+}
+
 /// Calculate the length of a nul-terminated string. Defers to C's `strlen` when possible.
 ///
 /// # Safety

tests/ui/associated-types/associated-types-in-ambiguous-context.stderr

@@ -49,10 +49,10 @@ LL - type X = std::ops::Deref::Target;
 LL + type X = <ByteString as Deref>::Target;
    |
 LL - type X = std::ops::Deref::Target;
-LL + type X = <CString as Deref>::Target;
+LL + type X = <CStr as Deref>::Target;
    |
 LL - type X = std::ops::Deref::Target;
-LL + type X = <IoSlice<'_> as Deref>::Target;
+LL + type X = <CString as Deref>::Target;
    |
      and N other candidates