better handling of get_mce_kill return value

TODO

@@ -0,0 +1,32 @@
+# TODO
+* after PR is made, create changelog
+* 32bit support?
+* fix https://github.com/nix-rust/nix/pull/1550/checks?check_run_id=4637943143
+  * https://cirrus-ci.com/task/6249061924732928
+
+
+# refactor
+* skriv helper functions för att deduplicera
+* red ut om c_int / c_ulong skall användas
+  * greppa på c_ulong?
+* maybeuninit memory alloc?
+
+
+# intressanta kodreferenser
+* sys/signal.rs wait() & killpg()
+
+
+# not implemented
+* capability stuff avoided
+* powerpc, arm64, mips etc. stuff avoided
+
+
+# questions
+* how many of the prctl options should be implemented, considering i do not have the means to test all architectures
+* should the naming be changed to be more user friendly, or remain as it is, as close to the original name as possible
+* which feature (if any) should prctl be under. and should it be enabled by default
+* should prctl be exported as unsafe function or not?
+
+
+# argumentation för min impl
+* nix unified syscalls

src/sys/prctl.rs

@@ -211,5 +211,8 @@ pub fn get_mce_kill() -> Result<PrctlMCEKillPolicy> {
         libc::prctl(PR_MCE_KILL_GET as c_int, 0, 0, 0, 0)
     };
 
-    Errno::result(res).map(|res| PrctlMCEKillPolicy::try_from(res).unwrap())
+    match Errno::result(res) {
+        Ok(val) => Ok(PrctlMCEKillPolicy::try_from(val)?),
+        Err(e) => Err(e),
+    }
 }