gradle-plugin: Rerun tasks if konan.home property is changes

#KT-20193 Fixed

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

@@ -96,8 +96,11 @@ open class KonanCompileTask: KonanTargetableTask() {
         internal set
 
     @Input var dumpParameters: Boolean = false
-    // TODO: Is there a better way to rerun tasks when the compiler version changes?
-    @Input val konanVersion = project.konanVersion
+
+    val konanVersion
+        @Input get() = project.konanVersion
+    val konanHome
+        @Input get() = project.konanHome
 
     // Task action ------------------------------------------------------------
 

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

@@ -65,7 +65,10 @@ open class KonanInteropTask: KonanTargetableTask() {
     @InputFiles val headers   = mutableSetOf<FileCollection>()
     @InputFiles val linkFiles = mutableSetOf<FileCollection>()
 
-    @Input val konanVersion = project.konanVersion
+    val konanVersion
+        @Input get() = project.konanVersion
+    val konanHome
+        @Input get() = project.konanHome
 
     @TaskAction
     fun exec() {

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

@@ -47,7 +47,7 @@ internal fun Project.setProperty(property: KonanPlugin.ProjectProperty, value: A
 internal val Project.konanHome: String
     get() {
         assert(hasProperty(KonanPlugin.ProjectProperty.KONAN_HOME))
-        return getProperty(KonanPlugin.ProjectProperty.KONAN_HOME).toString()
+        return project.file(getProperty(KonanPlugin.ProjectProperty.KONAN_HOME)).canonicalPath
     }
 
 internal val Project.konanBuildRoot               get() = "${buildDir.canonicalPath}/konan"