Fix VxWorks available parallelism: Move nonzero::uncheked into unsafe block

Author: biabbas

Diff for: std/src/sys/pal/unix/thread.rs

@@ -489,9 +489,11 @@ pub fn available_parallelism() -> io::Result<NonZero<usize>> {
                 fn vxCpuEnabledGet() -> libc::cpuset_t;
             }
 
-            // always fetches a valid bitmask
-            let set = unsafe { vxCpuEnabledGet() };
-            Ok(NonZero::new_unchecked(set.count_ones() as usize))
+            unsafe{
+                // always fetches a valid bitmask
+                let set = vxCpuEnabledGet();
+                Ok(NonZero::new_unchecked(set.count_ones() as usize))
+            }
         } else {
             // FIXME: implement on Redox, l4re
             Err(io::const_io_error!(io::ErrorKind::Unsupported, "Getting the number of hardware threads is not supported on the target platform"))