Add regression test for #6507

Author: nicolasstucki

tests/pos/i6507.scala

@@ -0,0 +1,9 @@
+object Test {
+  inline def s1 = 47 *: s2
+
+  inline def s2 = 48 *: s3
+
+  inline def s3 = 49 *: ()
+
+  s1
+}