Add comment about panic::set_hook() and reference cargo bug report

src/lib.rs

@@ -23,6 +23,11 @@ pub fn initialize(_argc: *const isize, _argv: *const *const *const u8) -> isize
     // Registers a panic hook that aborts the process before unwinding.
     // It is useful to abort before unwinding so that the fuzzer will then be
     // able to analyse the process stack frames to tell different bugs appart.
+    // 
+    // HACK / FIXME: it would be better to use `-C panic=abort` but it's currently
+    // impossible to build code using compiler plugins with this flag.
+    // We will be able to remove this code when
+    // https://github.com/rust-lang/cargo/issues/5423 is fixed.
     ::std::panic::set_hook(Box::new(|_| {
             ::std::process::abort();
     }));