Add the compiler classpath of the KotlinCompile task as KaptTask's input

KaptTask was not declaring the compiler classpath (which it takes from
compileKotlin task for calling the compiler) as input. This commit fixes
that and adds a test that checks compiler classpath input checks for the
kapt tasks.

Issue #KT-23879 Fixed

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/kotlin/org/jetbrains/kotlin/gradle/UpToDatenessIT.kt

@@ -72,7 +72,14 @@ class UpToDateIT : BaseGradleIT() {
         override fun initProject(project: Project) = with(project) {
             buildGradle.appendText("\nprintln 'compiler_cp=' + compileKotlin.getComputedCompilerClasspath\$kotlin_gradle_plugin()")
             build("clean") { originalCompilerCp = "compiler_cp=\\[(.*)]".toRegex().find(output)!!.groupValues[1].split(", ") }
-            buildGradle.appendText("\ncompileKotlin.compilerClasspath = files($originalPaths).toList()")
+            buildGradle.appendText("""${'\n'}
+                // Add Kapt to the project to test its input checks as well:
+                apply plugin: 'kotlin-kapt'
+                compileKotlin.compilerClasspath = files($originalPaths).toList()
+                afterEvaluate {
+                    kaptGenerateStubsKotlin.compilerClasspath = files($originalPaths).toList()
+                }
+            """.trimIndent())
         }
 
         override fun mutateProject(project: Project) = with(project) {
@@ -88,7 +95,7 @@ class UpToDateIT : BaseGradleIT() {
         }
 
         override fun checkAfterRebuild(compiledProject: CompiledProject) = with(compiledProject) {
-            assertTasksExecuted(listOf(":compileKotlin"))
+            assertTasksExecuted(listOf(":compileKotlin", ":kaptGenerateStubsKotlin", ":kaptKotlin"))
         }
     }