xfail std::num::complex::test_norm on x86, r=burningtree.

src/libextra/num/complex.rs

@@ -222,6 +222,8 @@ mod test {
     }
 
     #[test]
+    #[ignore(cfg(target_arch = "x86"))]
+    // FIXME #7158: (maybe?) currently failing on x86.
     fn test_norm() {
         fn test(c: Complex, ns: float) {
             assert_eq!(c.norm_sqr(), ns);