ObjCExport: use terminatingExceptionHandler by default

If something called from an ObjCExport bridge throws a Kotlin exception,
treat it as fatal by default and terminate the process.

This affects
* Runtime calls (managing and converting Kotlin and Obj-C references and
  other types), that shouldn't throw such exceptions anyway
* User code (Kotlin function object throws Kotlin exception when
  called from Swift/Obj-C).

If an exception should be handled non-fatally (e.g. forwarded to
the caller), this intention should be expressed in the code generator
explicitly.

^KT-50830

This change makes the code more simple and efficient,
and the control flow -- more explicit.

kotlin-native/backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/llvm/ContextUtils.kt

@@ -500,7 +500,7 @@ internal class Llvm(val context: Context, val llvmModule: LLVMModuleRef) : Runti
     val Kotlin_ObjCExport_AbstractClassConstructorCalled by lazyRtFunction
     val Kotlin_ObjCExport_RethrowExceptionAsNSError by lazyRtFunction
     val Kotlin_ObjCExport_WrapExceptionToNSError by lazyRtFunction
-    val Kotlin_ObjCExport_RethrowNSErrorAsException by lazyRtFunction
+    val Kotlin_ObjCExport_NSErrorAsException by lazyRtFunction
     val Kotlin_ObjCExport_AllocInstanceWithAssociatedObject by lazyRtFunction
     val Kotlin_ObjCExport_createContinuationArgument by lazyRtFunction
     val Kotlin_ObjCExport_createUnitContinuationArgument by lazyRtFunction

kotlin-native/backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/llvm/objcexport/ObjCExportCodeGenerator.kt

@@ -169,19 +169,13 @@ internal open class ObjCExportCodeGeneratorBase(codegen: CodeGenerator) : ObjCCo
         return callFromBridge(llvmDeclarations, args, resultLifetime)
     }
 
-    // TODO: currently bridges don't have any custom `landingpad`s,
-    // so it is correct to use [callAtFunctionScope] here.
-    // However, exception handling probably should be refactored
-    // (e.g. moved from `IrToBitcode.kt` to [FunctionGenerationContext]).
     fun ObjCExportFunctionGenerationContext.callFromBridge(
             function: LlvmCallable,
             args: List<LLVMValueRef>,
             resultLifetime: Lifetime = Lifetime.IRRELEVANT,
     ): LLVMValueRef {
-
-        // TODO: it is required only for Kotlin-to-Objective-C bridges.
-        this.forwardingForeignExceptionsTerminatedWith = objcTerminate
-        val exceptionHandler = ExceptionHandler.Caller
+        // All calls that actually do need to forward exceptions to callers should express this explicitly.
+        val exceptionHandler = terminatingExceptionHandler
 
         return call(function, args, resultLifetime, exceptionHandler)
     }
@@ -1251,8 +1245,12 @@ private fun ObjCExportCodeGenerator.generateKotlinToObjCBridge(
 
         fun rethrow() {
             val error = load(errorOutPtr!!)
-            callFromBridge(context.llvm.Kotlin_ObjCExport_RethrowNSErrorAsException, listOf(error))
-            unreachable()
+            val exception = callFromBridge(
+                    context.llvm.Kotlin_ObjCExport_NSErrorAsException,
+                    listOf(error),
+                    resultLifetime = Lifetime.THROW
+            )
+            ExceptionHandler.Caller.genThrow(this, exception)
         }
 
         fun genKotlinBaseMethodResult(

kotlin-native/runtime/src/main/cpp/ObjCExportErrors.mm

@@ -138,12 +138,6 @@ extern "C" OBJ_GETTER(Kotlin_ObjCExport_NSErrorAsException, id error) {
   RETURN_RESULT_OF(Kotlin_ObjCExport_NSErrorAsExceptionImpl, message, kotlinError);
 }
 
-extern "C" void Kotlin_ObjCExport_RethrowNSErrorAsException(id error) {
-    ObjHolder holder;
-    KRef exception = Kotlin_ObjCExport_NSErrorAsException(error, holder.slot());
-    ThrowException(exception);
-}
-
 @interface NSError (NSErrorKotlinException)
 @end;