gradle-plugin: Warn if both konan.home and konan.version are used

The gradle plugin ignores the `konan.version` property if the
`konan.home` one is set. This patch prints warning in such cases.

tools/kotlin-native-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/KonanCompilerDownloadTask.kt

@@ -45,6 +45,12 @@ open class KonanCompilerDownloadTask : DefaultTask() {
         if (!project.hasProperty(KonanPlugin.ProjectProperty.DOWNLOAD_COMPILER)) {
             val konanHome = project.getProperty(KonanPlugin.ProjectProperty.KONAN_HOME)
             logger.info("Use a user-defined compiler path: $konanHome")
+            if (project.hasProperty(KonanPlugin.ProjectProperty.KONAN_VERSION)) {
+                val konanVersion = project.getProperty(KonanPlugin.ProjectProperty.KONAN_VERSION)
+                logger.warn("${KonanPlugin.ProjectProperty.KONAN_VERSION.propertyName} " +
+                        "(=$konanVersion) property is ignored " +
+                        "because a user-defined compiler path is specified: $konanHome")
+            }
         } else {
             try {
                 val konanCompiler = project.konanCompilerName()