use File.pathSeparator for classpath in genDocs and dottydocs

- use File.pathSeparator instead of hard-coded path separator `:`
  => this way Windows user can run the command as well
- reduce code duplication: move classpath string generation to
  own function and reuse in genDocs and dottydocs

Author: robstoll

project/Build.scala

@@ -366,7 +366,7 @@ object Build {
 
       val dottyLib = (packageAll in `dotty-compiler`).value("dotty-library")
       val dottyInterfaces = (packageAll in `dotty-compiler`).value("dotty-interfaces")
-      val otherDeps = (dependencyClasspath in Compile).value.map(_.data).mkString(":")
+      val otherDeps = (dependencyClasspath in Compile).value.map(_.data).mkString(File.pathSeparator)
       val sources =
         (unmanagedSources in (Compile, compile)).value ++
           (unmanagedSources in (`dotty-compiler`, Compile)).value
@@ -375,7 +375,7 @@ object Build {
         "-project", "Dotty",
         "-project-version", dottyVersion,
         "-project-url", dottyGithubUrl,
-        "-classpath", s"$dottyLib:$dottyInterfaces:$otherDeps"
+        "-classpath", dottyLib + File.pathSeparator + dottyInterfaces + File.pathSeparator + otherDeps
       )
       (runMain in Compile).toTask(
         s""" dotty.tools.dottydoc.Main ${args.mkString(" ")} ${sources.mkString(" ")}"""
@@ -386,8 +386,8 @@ object Build {
       val args: Seq[String] = spaceDelimited("<arg>").parsed
       val dottyLib = (packageAll in `dotty-compiler`).value("dotty-library")
       val dottyInterfaces = (packageAll in `dotty-compiler`).value("dotty-interfaces")
-      val otherDeps = (dependencyClasspath in Compile).value.map(_.data).mkString(":")
-      val cp: Seq[String] = Seq("-classpath", s"$dottyLib:$dottyInterfaces:$otherDeps")
+      val otherDeps = (dependencyClasspath in Compile).value.map(_.data).mkString(File.pathSeparator)
+      val cp: Seq[String] = Seq("-classpath", dottyLib + File.pathSeparator + dottyInterfaces + File.pathSeparator + otherDeps)
         (runMain in Compile).toTask(s""" dotty.tools.dottydoc.Main ${cp.mkString(" ")} """ + args.mkString(" "))
     }.evaluated,