backend/tests: Add compilation logging

buildSrc/src/main/groovy/org/jetbrains/kotlin/KonanTest.groovy

@@ -38,6 +38,8 @@ abstract class KonanTest extends DefaultTask {
     abstract void compileTest(List<String> filesToCompile, String exe)
 
     protected void runCompiler(List<String> filesToCompile, String output, List<String> moreArgs) {
+        def log = new ByteArrayOutputStream()
+        try {
             project.javaexec {
                 main = 'org.jetbrains.kotlin.cli.bc.K2NativeKt'
                 classpath = project.configurations.cli_bc
@@ -48,7 +50,13 @@ abstract class KonanTest extends DefaultTask {
                         *filesToCompile,
                         *moreArgs,
                         *project.globalArgs)
-
+                standardOutput = log
+                errorOutput = log
+            }
+        } finally {
+            def logString = log.toString()
+            project.file("${output}.compilation.log").write(logString)
+            println(logString)
         }
     }
 
@@ -128,12 +136,6 @@ class RunExternalTestGroup extends RunKonanTest {
     String filter = project.findProperty("filter")
     String goldValue = "OK"
 
-    String buildExePath() {
-        def exeName = "${name}.kt.exe"
-        def tempDir = temporaryDir.absolutePath
-        return "$tempDir/$exeName"
-    }
-
     // TODO refactor
     List<String> buildCompileList() {
         def result = []