Check x86_64 size assertions on aarch64, too

This makes it easier for contributors on aarch64 workstations (e.g. Macs) to
notice when these assertions have been violated.

compiler/rustc_middle/src/traits/mod.rs

@@ -550,7 +550,7 @@ impl<'tcx> ObligationCauseCode<'tcx> {
 }
 
 // `ObligationCauseCode` is used a lot. Make sure it doesn't unintentionally get bigger.
-#[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
+#[cfg(all(any(target_arch = "x86_64", target_arch = "aarch64"), target_pointer_width = "64"))]
 static_assert_size!(ObligationCauseCode<'_>, 48);
 
 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]