Accept stale Predef symbol

Otherwise we'd get a "stale symbol error" when compiling stdLib in the community build.

Author: odersky

Diff for: compiler/src/dotty/tools/dotc/core/SymDenotations.scala

@@ -2457,10 +2457,12 @@ object SymDenotations {
 
   /** Possibly accept stale symbol with warning if in IDE */
   def acceptStale(denot: SingleDenotation)(using Context): Boolean =
-    staleOK && {
-      report.debugwarn(denot.staleSymbolMsg)
-      true
-    }
+    denot.symbol.sourceModule == defn.ScalaPredefModule
+    || staleOK
+        && {
+          report.debugwarn(denot.staleSymbolMsg)
+          true
+        }
 
 // ---- Completion --------------------------------------------------------