SI-7564 Fix detection of reflective calls on Avian

Base_1.scala checks whether reflection was used by inspecting
the stacktrace and looking for “java.lang.reflect.”.

The stacktrace looks differently on Avian and therefore the
test fails.

This change looks for “sun.reflect.” instead, which seems to
work on OpenJDK and Avian.

Author: soc

test/files/run/t3425b/Base_1.scala

@@ -9,7 +9,7 @@ class ABC extends A with B with C {
   private def reflected = (
     Thread.currentThread.getStackTrace
       takeWhile (_.getMethodName != "main")
-      exists (_.toString contains "java.lang.reflect.")
+      exists (_.toString contains "sun.reflect.")
   )
   lazy val y: PQ = new PQ(reflected)
 }