Add nativeMultithreading in ScalaNativeModule (#3896)

- Remove dead code for Scala Native 0.4
- Cleanup unused imports

Pull Request: #3896

scalanativelib/src/mill/scalanativelib/ScalaNativeModule.scala

@@ -220,6 +220,13 @@ trait ScalaNativeModule extends ScalaModule { outer =>
   /** Build target for current compilation */
   def nativeBuildTarget: T[BuildTarget] = Task { BuildTarget.Application }
 
+  /**
+   * Shall be compiled with multithreading support. If equal to `None` the
+   *  toolchain would detect if program uses system threads - when not thrads
+   *  are not used, the program would be linked without multihreading support.
+   */
+  def nativeMultithreading: T[Option[Boolean]] = Task { None }
+
   private def nativeConfig: Task[NativeConfig] = Task.Anon {
     val classpath = runClasspath().map(_.path).filter(_.toIO.exists).toList
 
@@ -240,6 +247,7 @@ trait ScalaNativeModule extends ScalaModule { outer =>
       nativeEmbedResources(),
       nativeIncrementalCompilation(),
       nativeDump(),
+      nativeMultithreading(),
       toWorkerApi(logLevel()),
       toWorkerApi(nativeBuildTarget())
     ) match {

scalanativelib/test/src/mill/scalanativelib/CompileRunTests.scala

@@ -2,7 +2,6 @@ package mill.scalanativelib
 
 import java.util.jar.JarFile
 import mill._
-import mill.api.Result
 import mill.define.Discover
 import mill.eval.EvaluatorPaths
 import mill.scalalib.api.ZincWorkerUtil

scalanativelib/test/src/mill/scalanativelib/TestingTests.scala

@@ -2,20 +2,11 @@ package mill.scalanativelib
 
 import mill._
 import mill.api.Result
-import mill.define.Discover
-import mill.eval.EvaluatorPaths
-import mill.scalalib.api.ZincWorkerUtil
-import mill.scalalib.publish.{Developer, License, PomSettings, VersionControl}
-import mill.scalalib.{DepSyntax, PublishModule, ScalaModule, TestModule}
 import mill.scalanativelib.api._
-import mill.testkit.{TestBaseModule, UnitTester}
+import mill.testkit.UnitTester
 import mill.testrunner.TestResult
-import mill.util.TestUtil
 import utest._
 
-import java.util.jar.JarFile
-import scala.jdk.CollectionConverters._
-
 object TestingTests extends TestSuite {
   import CompileRunTests._
   def tests: Tests = Tests {

scalanativelib/worker-api/src/mill/scalanativelib/worker/api/ScalaNativeWorkerApi.scala

@@ -27,6 +27,7 @@ private[scalanativelib] trait ScalaNativeWorkerApi {
       nativeEmbedResources: Boolean,
       nativeIncrementalCompilation: Boolean,
       nativeDump: Boolean,
+      nativeMultithreading: Option[Boolean],
       logLevel: NativeLogLevel,
       buildTarget: BuildTarget
   ): Either[String, Object]

scalanativelib/worker/0.5/src/mill/scalanativelib/worker/ScalaNativeWorkerImpl.scala

@@ -58,6 +58,7 @@ class ScalaNativeWorkerImpl extends mill.scalanativelib.worker.api.ScalaNativeWo
       nativeEmbedResources: Boolean,
       nativeIncrementalCompilation: Boolean,
       nativeDump: Boolean,
+      nativeMultithreading: Option[Boolean],
       logLevel: NativeLogLevel,
       buildTarget: BuildTarget
   ): Either[String, Config] = {
@@ -81,6 +82,7 @@ class ScalaNativeWorkerImpl extends mill.scalanativelib.worker.api.ScalaNativeWo
         })
         .withEmbedResources(nativeEmbedResources)
         .withIncrementalCompilation(nativeIncrementalCompilation)
+        .withMultithreading(nativeMultithreading)
         .withBaseName("out")
 
     val config = Config.empty