avoid boxing

scala.runtime.Rich{Double, Float} has `isNaN` and these are value class.
Also java.lang.{Double, Float} has `isNaN`.

- https://docs.oracle.com/javase/8/docs/api/java/lang/Double.html#isNaN--
- https://docs.oracle.com/javase/8/docs/api/java/lang/Float.html#isNaN--

We can't call `RichDouble#isNaN` because
`implicit def double2Double(x: Double): java.lang.Double`
is higher priority than
`implicit def doubleWrapper(x: Double): RichDouble`

```
$ scala -version
Scala code runner version 2.11.8 -- Copyright 2002-2016, LAMP/EPFL

$ scala -Xprint:jvm -e "1.0.isNaN"
[[syntax trees at end of                       jvm]] // scalacmd616162202928036892.scala
package <empty> {
  object Main extends Object {
    def main(args: Array[String]): Unit = {
      new <$anon: Object>();
      ()
    };
    def <init>(): Main.type = {
      Main.super.<init>();
      ()
    }
  };
  final class anon$1 extends Object {
    def <init>(): <$anon: Object> = {
      anon$1.super.<init>();
      scala.this.Predef.double2Double(1.0).isNaN();
      ()
    }
  }
}
```

1 files changed, 2 insertions, 2 deletions

diff --git a/src/reflect/scala/reflect/internal/Constants.scala b/src/reflect/scala/reflect/internal/Constants.scala
index 7b47798ff7..cd2debfaf4 100644
--- a/src/reflect/scala/reflect/internal/Constants.scala
+++ b/src/reflect/scala/reflect/internal/Constants.scala
@@ -87,8 +87,8 @@ trait Constants extends api.Constants {
     }
 
     def isNaN = value match {
-      case f: Float  => f.isNaN
-      case d: Double => d.isNaN
+      case f: Float  => java.lang.Float.isNaN(f)
+      case d: Double => java.lang.Double.isNaN(d)
       case _ => false
     }