backend/tests: Generate external test tasks in config stage

We generate tasks for external tests group during Gradle's configuration
phase instead of using separate task (regenerate_external_tests)

backend.native/tests/build.gradle

@@ -10,16 +10,17 @@ dependencies {
 }
 
 def testOutputRoot = rootProject.file("test.output").absolutePath
+def externalTestsDir = project.file("external")
 
 allprojects {
     // Root directories for test output (logs, compiled files, statistics etc). Only single path must be in each set.
     sourceSets {
-        // :backend.native:tests
+        // backend.native/tests
         testOutputLocal {
            output.dir(rootProject.file("$testOutputRoot/local"))
         }
 
-        // :backend.native:tests:external
+        // backend.native/tests/external
         testOutputExternal {
             output.dir(rootProject.file("$testOutputRoot/external"))
         }
@@ -32,63 +33,28 @@ task clean {
     }
 }
 
-task regenerate_external_tests() {
-    doLast {
-        def externalTestsProject = childProjects["external"]
-        def gradleGenerated = externalTestsProject.file("build.gradle")
-        def externalTestsDir = externalTestsProject.file("codegen/blackbox")
-        gradleGenerated.write("import org.jetbrains.kotlin.*\n")
-        gradleGenerated.append(
-"""
-/*******************************************************************************
-*      WARNING: This file auto generated with command 
-*      # ./gradlew  :backend.native:tests:regenerate_external_tests
-*******************************************************************************/
-configurations {
-    cli_bc
-}
-
-dependencies {
-    cli_bc project(path: ':backend.native', configuration: 'cli_bc')
-}
-"""
-        )
-        externalTestsDir.eachDirRecurse {
-            // Skip build directory and directories without *.kt files.
-            if (it.name == "build" || it.listFiles().count {it.name.endsWith(".kt")} == 0) {
-                return
-            }
-
-            def taskDirectory = externalTestsProject.relativePath(it)
-            def taskName = taskDirectory.replaceAll("[-/]", '_')
-
-            gradleGenerated.append(
-                    "task $taskName (type: RunExternalTestGroup) {\n" +
-                    "   groupDirectory = \"$taskDirectory\"\n" +
-                    "}\n\n")
-        }
-        gradleGenerated.append(
-"""
-task daily {
-    dependsOn(codegen_blackbox_annotations)
-}
-
 task run() {
-    dependsOn(tasks.withType(RunExternalTestGroup).matching { it.enabled })
-}
-"""
-        )
-    }
-}
-
-task run() {
-    dependsOn(tasks.withType(KonanTest).matching { it.enabled })
+    dependsOn(tasks.withType(KonanTest).matching { !(it instanceof RunExternalTestGroup) && it.enabled })
 }
 
 task run_external () {
     // TODO Consider test output directory cleaning before execution.
     // TODO Consider using some logger instead of println
-    def testTasks = childProjects["external"].tasks.withType(RunExternalTestGroup).matching { it.enabled }
+    // Create tasks for external tests
+    externalTestsDir.eachDirRecurse {
+        // Skip build directory and directories without *.kt files.
+        if (it.name == "build" || it.listFiles().count {it.name.endsWith(".kt")} == 0) {
+            return
+        }
+
+        def taskDirectory = project.relativePath(it)
+        def taskName = taskDirectory.replaceAll("[-/]", '_')
+
+        task("$taskName", type: RunExternalTestGroup){
+            groupDirectory = "$taskDirectory"
+        }
+    }
+    def testTasks = tasks.withType(RunExternalTestGroup).matching { it.enabled }
     dependsOn(testTasks)
 
     doLast {
@@ -111,6 +77,10 @@ task run_external () {
     }
 }
 
+task daily() {
+    dependsOn(run_external)
+}
+
 task sum (type:RunKonanTest) {
     source = "codegen/function/sum.kt"
 }