Add -scala-release flag

Author: Kordyjan

compiler/src/dotty/tools/dotc/config/ScalaSettings.scala

@@ -101,6 +101,7 @@ trait CommonScalaSettings:
   val silentWarnings: Setting[Boolean] = BooleanSetting("-nowarn", "Silence all warnings.", aliases = List("--no-warnings"))
 
   val release: Setting[String] = ChoiceSetting("-release", "release", "Compile code with classes specific to the given version of the Java platform available on the classpath and emit bytecode for this version.", ScalaSettings.supportedReleaseVersions, "", aliases = List("--release"))
+  val scalaRelease: Setting[String] = ChoiceSetting("-scala-release", "release", "Emit TASTy files that can be consumed by specified version of the compiler.", List("3.0", "3.1"), "3.1", aliases = List("--scala-release"))
   val deprecation: Setting[Boolean] = BooleanSetting("-deprecation", "Emit warning and location for usages of deprecated APIs.", aliases = List("--deprecation"))
   val feature: Setting[Boolean] = BooleanSetting("-feature", "Emit warning and location for usages of features that should be imported explicitly.", aliases = List("--feature"))
   val explain: Setting[Boolean] = BooleanSetting("-explain", "Explain errors in more detail.", aliases = List("--explain"))

compiler/test/dotty/tools/vulpix/ParallelTesting.scala

@@ -215,10 +215,11 @@ trait ParallelTesting extends RunnerOrchestration { self =>
 
         case testSource @ SeparateCompilationSource(_, dir, flags, outDir) =>
           testSource.compilationGroups.map { (group, files) =>
+            val flags1 = if group.target.isEmpty then flags else flags.and("-scala-release", group.target)
             if group.compiler.isEmpty then
-              compile(files, flags, suppressErrors, outDir)
+              compile(files, flags1, suppressErrors, outDir)
             else
-              compileWithOtherCompiler(group.compiler, files, flags, outDir)
+              compileWithOtherCompiler(group.compiler, files, flags1, outDir)
           }
       })