Do not check java trait secondary constructors

See tests/pos/i851.java

Author: nicolasstucki

compiler/src/dotty/tools/dotc/typer/Checking.scala

@@ -440,8 +440,8 @@ object Checking {
     }
     if (sym.isValueClass && sym.is(Trait) && !sym.isRefinementClass)
       fail(CannotExtendAnyVal(sym))
-    if (sym.isConstructor && !sym.isPrimaryConstructor && sym.owner.is(Trait))
-      fail("Traits cannot have secondary constructors")
+    if (sym.isConstructor && !sym.isPrimaryConstructor && sym.owner.is(Trait, butNot = JavaDefined))
+      fail("Traits cannot have secondary constructors " + sym.owner.flagsString)
     checkCombination(Final, Open)
     checkCombination(Sealed, Open)
     checkCombination(Final, Sealed)