Make fpreg_t an union

Author: kellda

libc-test/build.rs

@@ -4811,8 +4811,6 @@ fn test_linux(target: &str) {
     cfg.skip_roundtrip(move |s| match s {
         // FIXME(1.0):
         "mcontext_t" if s390x => true,
-        // FIXME(union): This is actually a union.
-        "fpreg_t" if s390x => true,
 
         // The test doesn't work on some env:
         "ipv6_mreq"

src/unix/linux_like/linux/gnu/b64/s390x.rs

@@ -212,18 +212,17 @@ s! {
 }
 
 s_no_extra_traits! {
-    // FIXME(union): This is actually a union.
-    pub struct fpreg_t {
+    pub union fpreg_t {
         pub d: c_double,
-        // f: c_float,
+        pub f: c_float,
     }
 }
 
 cfg_if! {
     if #[cfg(feature = "extra_traits")] {
         impl PartialEq for fpreg_t {
             fn eq(&self, other: &fpreg_t) -> bool {
-                self.d == other.d
+                unimplemented!("traits")
             }
         }