Elide message def binding if not used

This also reduces sligttly the size of the if it is used.
Also make `assertFail` private.

Author: nicolasstucki

library/src/dotty/DottyPredef.scala

@@ -3,18 +3,18 @@ package dotty
 object DottyPredef {
   import compiletime.summonFrom
 
-  inline final def assert(assertion: => Boolean, message: => Any): Unit = {
+  inline final def assert(inline assertion: Boolean, inline message: => Any): Unit = {
     if (!assertion)
       assertFail(message)
   }
 
-  inline final def assert(inline assertion: => Boolean) <: Unit = {
+  inline final def assert(inline assertion: Boolean): Unit = {
     if (!assertion)
       assertFail()
   }
 
-  def assertFail(): Nothing = throw new java.lang.AssertionError("assertion failed")
-  def assertFail(message: => Any): Nothing = throw new java.lang.AssertionError("assertion failed: " + message)
+  private def assertFail(): Nothing = throw new java.lang.AssertionError("assertion failed")
+  private def assertFail(message: => Any): Nothing = throw new java.lang.AssertionError("assertion failed: " + message)
 
   inline final def implicitly[T](implicit ev: T): T = ev