Add some minor souper-harvested optimizations (#5735)

I was playing around with souper recently on some wasms I had lying
around and these are some optimization opportunities that popped out
which seemed easy-enough to add to the egraph-based optimizations.

cranelift/codegen/src/opts/cprop.isle

@@ -110,6 +110,10 @@
        (bxor ty k @ (iconst ty _) x))
       (bxor ty x k))
 
+(rule (simplify
+       (icmp ty cc k @ (iconst _ _) x))
+      (icmp ty (intcc_reverse cc) x k))
+
 ;; Canonicalize via associativity: reassociate to a right-heavy tree
 ;; for constants.
 ;;