Fix the type of the 'f_fsid' field in 'struct statvfs'.

(backport <rust-lang#4576>)
(cherry picked from commit d98eb8f)

Author: Xing Xue

libc-test/build.rs

@@ -5700,6 +5700,9 @@ fn test_aix(target: &str) {
             ("__context64", "fpr") => true,
             ("__tm_context_t", "fpr") => true,
 
+            // The _ALL_SOURCE type of 'f_fsid' differs from POSIX's on AIX.
+            ("statvfs", "f_fsid") => true,
+
             _ => false,
         }
     });

src/unix/aix/powerpc64.rs

@@ -29,7 +29,7 @@ s! {
         pub f_files: crate::fsfilcnt_t,
         pub f_ffree: crate::fsfilcnt_t,
         pub f_favail: crate::fsfilcnt_t,
-        pub f_fsid: crate::fsid_t,
+        pub f_fsid: c_ulong,
         pub f_basetype: [c_char; 16],
         pub f_flag: c_ulong,
         pub f_namemax: c_ulong,