runtime: use exitStatus == 1 if main finished with exception

Also update the corresponding test.

backend.native/tests/build.gradle

@@ -1141,6 +1141,7 @@ task spread_operator_0(type: RunKonanTest) {
 task main_exception(type: RunKonanTest) {
     // TODO: cannot currently check the output because the exact stacktrace strings are unpredictable.
     // goldValue = "Uncaught exception from Kotlin's main: Throwable\n"
+    expectedExitStatus = 1
     source = "runtime/basic/main_exception.kt"
 }
 

runtime/src/launcher/cpp/launcher.cpp

@@ -18,19 +18,23 @@ OBJ_GETTER(setupArgs, int argc, char** argv) {
 }
 
 //--- main --------------------------------------------------------------------//
-extern "C" void Konan_start(const ObjHeader* );
+extern "C" KInt Konan_start(const ObjHeader* );
 
 int main(int argc, char** argv) {
   RuntimeState* state = InitRuntime();
 
-  if (state != nullptr) {
+  if (state == nullptr) {
+    return 2;
+  }
+
+  KInt exitStatus;
+  {
     ObjHolder args;
     setupArgs(argc, argv, args.slot());
-    Konan_start(args.obj());
+    exitStatus = Konan_start(args.obj());
   }
 
   DeinitRuntime(state);
 
-  // Yes, we have to follow Java convention and return zero.
-  return 0;
+  return exitStatus;
 }

runtime/src/launcher/kotlin/konan/start.kt

@@ -3,16 +3,19 @@ import konan.internal.ExportForCppRuntime
 external fun main(args: Array<String>)
 
 @ExportForCppRuntime
-private fun Konan_start(args: Array<String>) {
+private fun Konan_start(args: Array<String>): Int {
     try {
 
         // This is kotlin program main entry point
         main(args)
 
+        // Successfully finished:
+        return 0
+
     } catch (e: Throwable) {
         // TODO: may be add some more info.
         print("Uncaught exception from Kotlin's main: ")
         e.printStackTrace()
-        // TODO: should exit with non-zero code.
+        return 1
     }
 }