Remove multiversal variants of ==

Map them to Any_==, which is the only method supported
by the backend.

Author: odersky

src/dotty/tools/dotc/transform/InterceptedMethods.scala

@@ -100,6 +100,7 @@ class InterceptedMethods extends MiniPhaseTransform {
     lazy val Select(qual, _) = tree.fun
     val Any_## = this.Any_##
     val Any_!= = defn.Any_!=
+    val Any_null_== = defn.Any_null_==
     val rewrite: Tree = tree.fun.symbol match {
       case Any_## =>
           poundPoundValue(qual)
@@ -113,6 +114,8 @@ class InterceptedMethods extends MiniPhaseTransform {
               List(qual, typer.resolveClassTag(tree.pos, qual.tpe.widen))))
           }*/
          */
+      case Any_null_== =>
+          qual.select(defn.Any_==).appliedToArgs(tree.args)
       case t if primitiveGetClassMethods.contains(t) =>
           // if we got here then we're trying to send a primitive getClass method to either
           // a) an Any, in which cage Object_getClass works because Any erases to object. Or
@@ -123,6 +126,8 @@ class InterceptedMethods extends MiniPhaseTransform {
           //    so we need replace that method name with Object_getClass to get correct behavior.
           //    See SI-5568.
           qual.selectWithSig(defn.Any_getClass).appliedToNone
+      case t if t.name == nme.EQ && t.owner == defn.NullClass =>
+        qual.select(defn.Any_==).appliedToArgs(tree.args)
       case _ =>
         tree
     }