Correct musl si_value extractor

Author: Douman

src/unix/linux_like/linux/musl/mod.rs

@@ -32,6 +32,8 @@ impl siginfo_t {
             _si_signo: ::c_int,
             _si_errno: ::c_int,
             _si_code: ::c_int,
+            _si_timerid: ::c_int,
+            _si_overrun: ::c_int,
             si_value: ::sigval,
         }