Add helper for getting an int out of a Scalar

compiler/rustc_middle/src/mir/interpret/value.rs

@@ -357,6 +357,14 @@ impl<'tcx, Tag> Scalar<Tag> {
         self.to_bits(target_size).expect("expected Raw bits but got a Pointer")
     }
 
+    #[inline]
+    pub fn assert_int(self) -> ScalarInt {
+        match self {
+            Scalar::Ptr(_) => bug!("expected an int but got an abstract pointer"),
+            Scalar::Int(int) => int,
+        }
+    }
+
     #[inline]
     pub fn assert_ptr(self) -> Pointer<Tag> {
         match self {