[nomaster] revives BuildUtils.emptyValDef

That method was unnecessary in the first place, because we already had
emptyValDef in scala.reflect.api.Trees: https://github.com/scala/scala/blob/v2.10.0/src/reflect/scala/reflect/api/Trees.scala#L2367.
That's a rudiment from the times when we were unsure what to put into
scala.reflect.base and what goes into scala.reflect.api.

Unfortunately, it's not just a harmless extraneous method. Reifier v2.10.0
emits `u.build.emptyValDef` when it needs to reify `emptyValDef`. Therefore
we need to restore it to be forward compatible.

However we don't need to rollback the changes to the reifier v2.10.1,
which now simply calls `u.emptyValDef`, because, as mentioned above,
that `emptyValDef` was already there in v2.10.0.

2 files changed, 4 insertions, 0 deletions

diff --git a/src/reflect/scala/reflect/api/BuildUtils.scala b/src/reflect/scala/reflect/api/BuildUtils.scala
index 8f256aa1f5..0c8e81a220 100644
--- a/src/reflect/scala/reflect/api/BuildUtils.scala
+++ b/src/reflect/scala/reflect/api/BuildUtils.scala
@@ -59,6 +59,8 @@ private[reflect] trait BuildUtils { self: Universe =>
 
     def flagsFromBits(bits: Long): FlagSet
 
+    def emptyValDef: ValDef
+
     def This(sym: Symbol): Tree
 
     def Select(qualifier: Tree, sym: Symbol): Select
diff --git a/src/reflect/scala/reflect/internal/BuildUtils.scala b/src/reflect/scala/reflect/internal/BuildUtils.scala
index b1b0c5b60b..9f41f0336e 100644
--- a/src/reflect/scala/reflect/internal/BuildUtils.scala
+++ b/src/reflect/scala/reflect/internal/BuildUtils.scala
@@ -47,6 +47,8 @@ trait BuildUtils { self: SymbolTable =>
 
     def flagsFromBits(bits: Long): FlagSet = bits
 
+    def emptyValDef: ValDef = self.emptyValDef
+
     def This(sym: Symbol): Tree = self.This(sym)
 
     def Select(qualifier: Tree, sym: Symbol): Select = self.Select(qualifier, sym)