style: Workaround LLVM ABI bug.

All the gory details in https://bugzilla.mozilla.org/show_bug.cgi?id=1600735 and
related LLVM / GCC bugs. Avoid the issue by forcing the relevant enum to be
32-bit wide, so as to not trigger the LLVM bug.

Differential Revision: https://phabricator.services.mozilla.com/D57868

components/style/properties/properties.mako.rs

@@ -1803,8 +1803,11 @@ impl ToCss for PropertyId {
 }
 
 /// The counted unknown property list which is used for css use counters.
+///
+/// FIXME: This should be just #[repr(u8)], but can't be because of ABI issues,
+/// see https://bugs.llvm.org/show_bug.cgi?id=44228.
 #[derive(Clone, Copy, Debug, Eq, FromPrimitive, Hash, PartialEq)]
-#[repr(u8)]
+#[repr(u32)]
 pub enum CountedUnknownProperty {
     % for prop in data.counted_unknown_properties:
     /// ${prop.name}