x64 backend: migrate stores, and remainder of loads (I128 case), to ISLE. (#4069)

cranelift/codegen/src/isa/x64/lower/isle.rs

@@ -544,6 +544,11 @@ where
             None
         }
     }
+
+    #[inline]
+    fn amode_offset(&mut self, addr: &Amode, offset: u32) -> Amode {
+        addr.offset(offset)
+    }
 }
 
 // Since x64 doesn't have 8x16 shifts and we must use a 16x8 shift instead, we