Test --cross with the compile sub-command

Author: Gedochao

modules/integration/src/test/scala/scala/cli/integration/CompileTestsDefault.scala

@@ -1,4 +1,15 @@
 package scala.cli.integration
 
 class CompileTestsDefault extends CompileTestDefinitions with CompileTests3StableDefinitions
-    with TestDefault
+    with TestDefault {
+  test(
+    s"compile --cross $actualScalaVersion with ${Constants.scala213} and ${Constants.scala212}"
+  ) {
+    val crossVersions = Seq(actualScalaVersion, Constants.scala213, Constants.scala212)
+    simpleInputs
+      .add(os.rel / "project.scala" -> s"//> using scala ${crossVersions.mkString(" ")}")
+      .fromRoot { root =>
+        os.proc(TestUtil.cli, "compile", ".", "--cross", "--power", extraOptions).call(cwd = root)
+      }
+  }
+}