restore known failure

Author: tgross35

builtins-test/tests/conv.rs

@@ -75,8 +75,12 @@ mod i_to_f {
                         }
 
                         // Test against native conversion. We disable testing on all `x86` because of
-                        // rounding bugs with `i686`.
-                        if !Float::eq_repr(f0, f1) && !cfg!(target_arch = "x86") {
+                        // rounding bugs with `i686`. `powerpc` also has the same rounding bug.
+                        if !Float::eq_repr(f0, f1) && !cfg!(any(
+                            target_arch = "x86",
+                            target_arch = "powerpc",
+                            target_arch = "powerpc64"
+                        )) {
                             panic!(
                                 "{}({}): std: {:?}, builtins: {:?}",
                                 stringify!($fn),