aix: Resolve function comparison and unnecessary_transmutes warnings

(backport <#4780>)
(cherry picked from commit c819173)

Author: tgross35

src/unix/aix/mod.rs

@@ -326,6 +326,8 @@ s! {
         pub cmsg_type: c_int,
     }
 
+    // FIXME(1.0): This should not implement `PartialEq`
+    #[allow(unpredictable_function_pointer_comparisons)]
     pub struct sigevent {
         pub sigev_value: crate::sigval,
         pub sigev_signo: c_int,

src/unix/aix/powerpc64.rs

@@ -448,7 +448,7 @@ cfg_if! {
 
         impl hash::Hash for fpreg_t {
             fn hash<H: hash::Hasher>(&self, state: &mut H) {
-                let d: u64 = unsafe { mem::transmute(self.d) };
+                let d: u64 = self.d.to_bits();
                 d.hash(state);
             }
         }