add scc_block to MachineState to avoid SCC cleanup terms being deallocated too early (#1427)

src/parser/ast.rs

@@ -502,6 +502,12 @@ impl Fixnum {
             .with_f(false)
     }
 
+    #[inline]
+    pub fn get_tag(&self) -> HeapCellValueTag {
+        use modular_bitfield::Specifier;
+        HeapCellValueTag::from_bytes(self.tag()).unwrap()
+    }
+
     #[inline]
     pub fn build_with_checked(num: i64) -> Result<Self, OutOfBounds> {
         const UPPER_BOUND: i64 = (1 << 55) - 1;