Improve static elision of outer tests in pattern matcher

When the binder's info is a bounded type, look at the prefix of the
upper bound.

This stops an annoying unchecked warning that appeared since
a recent refactoring made `TermName` a final class. It also avoids
a needless runtime check.

src/compiler/scala/tools/nsc/transform/patmat/MatchTreeMaking.scala

@@ -349,7 +349,17 @@ trait MatchTreeMaking extends MatchCodeGen with Debugging {
 
         override def withOuterTest(orig: Tree)(testedBinder: Symbol, expectedTp: Type): Tree = {
           val expectedPrefix = expectedTp.prefix
-          val testedPrefix = testedBinder.info.prefix
+          def prefixOf(tp: Type): Type = tp.normalize match {
+            case RefinedType(parents, _) =>
+              val temp1 = parents.filterNot(_.typeSymbol.isStatic)
+              val temp2 = temp1.map(sym => prefixOf(sym))
+              temp2.distinct match {
+                case prefix :: Nil => prefix
+                case _ => NoType
+              }
+            case tp => tp.prefix
+          }
+          val testedPrefix = prefixOf(abstractTypesToBounds(testedBinder.info))
 
           // Check if a type is defined in a static location. Unlike `tp.isStatic` before `flatten`,
           // this also includes methods and (possibly nested) objects inside of methods.

test/files/pos/t11534.flags

@@ -0,0 +1 @@
+-Xfatal-warnings -unchecked

test/files/pos/t11534.scala

@@ -0,0 +1,7 @@
+object Test1 {
+    val g: scala.tools.nsc.Global = ???
+    import g._
+    def test(sym: Symbol) = sym.name match {
+        case _: TermName  =>
+    }
+}