Build.sbt: avoid compiling dotty twice at the same time

I added custom tasks to do `dotty/publishLocal` before
calling `update` on any of the bootstrapped project, but somehow this
resulted in the same compile task being run twice at the same time, now
the custom task is only added to `dotty-library-bootstrapped/update`.
`dotty-compiler-bootstrapped/update` depends on
`dotty-library-bootstrapped/update` so this is okay.

Author: smarter

project/Build.scala

@@ -94,15 +94,6 @@ object DottyBuild extends Build {
     scalaCompilerBridgeSource :=
       (dottyOrganization % "dotty-sbt-bridge" % scalaVersion.value % "component").sources(),
 
-    // The non-bootstrapped compiler needs to be published first.
-    update <<= update.dependsOn(Def.task {
-      // This crazy stuff is equivalent to `dotty/publishLocal`, if we just did
-      // `publishLocal in dotty` the aggregated projects would be ignored.
-      val s = state.value
-      val e = Project.extract(s)
-      e.runAggregated(publishLocal in dotty, s)
-    }),
-
     // sbt gets very unhappy if two projects use the same target
     target := baseDirectory.value / ".." / "out" / name.value
   )
@@ -439,7 +430,17 @@ object DottyBuild extends Build {
   lazy val `dotty-library-bootstrapped` = project.in(file("library")).
     settings(sourceStructure).
     settings(commonBootstrappedSettings).
-    settings(dottyLibrarySettings)
+    settings(dottyLibrarySettings).
+    settings(
+      // The non-bootstrapped compiler needs to be published first.
+      update <<= update.dependsOn(Def.task {
+        // This crazy stuff is equivalent to `dotty/publishLocal`, if we just did
+        // `publishLocal in dotty` the aggregated projects would be ignored.
+        val s = state.value
+        val e = Project.extract(s)
+        e.runAggregated(publishLocal in dotty, s)
+      })
+    )
 
   // until sbt/sbt#2402 is fixed (https://github.com/sbt/sbt/issues/2402)
   lazy val cleanSbtBridge = TaskKey[Unit]("cleanSbtBridge", "delete dotty-sbt-bridge cache")