Only assert the Parser size on specific arches

The size of this struct depends on the alignment of `u128`, for example
powerpc64le and s390x have align-8 and end up with only 280 bytes. Our
64-bit tier-1 arches are the same though, so let's just assert on those.

compiler/rustc_parse/src/parser/mod.rs

@@ -189,8 +189,9 @@ pub struct Parser<'a> {
 }
 
 // This type is used a lot, e.g. it's cloned when matching many declarative macro rules with
-// nonterminals. Make sure it doesn't unintentionally get bigger.
-#[cfg(all(target_pointer_width = "64", not(target_arch = "s390x")))]
+// nonterminals. Make sure it doesn't unintentionally get bigger. We only check a few arches
+// though, because `TokenTypeSet(u128)` alignment varies on others, changing the total size.
+#[cfg(all(target_pointer_width = "64", any(target_arch = "aarch64", target_arch = "x86_64")))]
 rustc_data_structures::static_assert_size!(Parser<'_>, 288);
 
 /// Stores span information about a closure.