Merge pull request scala#9694 from retronym/topic/slash-syntax-stragglers

Avoid deprectated DSL in SBT build in two more places

Author: dwijnand

project/build.sbt

@@ -1,2 +1,2 @@
 // Add genprod to the build; It should be moved from `src/build` to `project` now that the Ant build is gone
-sources in Compile += ((baseDirectory).value.getParentFile / "src" / "build" / "genprod.scala")
+Compile / sources += ((baseDirectory).value.getParentFile / "src" / "build" / "genprod.scala")

project/plugins.sbt

@@ -12,7 +12,7 @@ enablePlugins(BuildInfoPlugin)
 
 lazy val buildClasspath = taskKey[String]("Colon-separated (or semicolon-separated in case of Windows) list of entries on the sbt build classpath.")
 
-buildClasspath := (externalDependencyClasspath in Compile).value.map(_.data).mkString(java.io.File.pathSeparator)
+buildClasspath := (Compile / externalDependencyClasspath).value.map(_.data).mkString(java.io.File.pathSeparator)
 
 buildInfoKeys := Seq[BuildInfoKey](buildClasspath)