Correct/simplify =:= implementation.

Can only guess that it dates back to before we had an nqp::eqaddr.

src/core/Mu.pm

@@ -611,7 +611,7 @@ multi sub infix:<~~>(Mu \topic, Mu \matcher) {
 proto sub infix:<=:=>(Mu $a?, Mu $b?) { * }
 multi sub infix:<=:=>($a?)      { Bool::True }
 multi sub infix:<=:=>(Mu \a, Mu \b) { 
-    nqp::p6bool(nqp::iseq_i(nqp::where(a), nqp::where(b)));
+    nqp::p6bool(nqp::eqaddr(a, b));
 }
 
 proto sub infix:<eqv>(Any $?, Any $?) { * }