re-enable tests for #1058 and #1059

Author: nikomatsakis

src/test/run-pass/c-stack-as-value.rs

@@ -1,5 +1,3 @@
-// xfail-test
-
 #[abi = "cdecl"]
 native mod rustrt {
     fn unsupervise();

src/test/run-pass/invoke-external-native.rs

@@ -1,5 +1,4 @@
-// xfail-test
-
+use std;
 import std::sys;
 
 // The purpose of this test is to check that we can
@@ -8,4 +7,4 @@ import std::sys;
 
 fn main() {
     let foo = sys::rustrt::last_os_error();
-}
+}