Don't crash trying to use --snapshot-kind=app-aot from 'dart' rather than 'dart_bootstrap'.

runtime/vm/dart_api_impl.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "include/dart_api.h"
 #include "include/dart_mirrors_api.h"
 #include "include/dart_native_api.h"
 
 #include "platform/assert.h"
 #include "lib/stacktrace.h"
@@ skipping 6308 matching lines @@
   thread->SetName(name);
 }
 
 
 // The precompiler is included in dart_bootstrap and dart_noopt, and
 // excluded from dart and dart_precompiled_runtime.
 #if !defined(DART_PRECOMPILER)
 
 DART_EXPORT Dart_Handle
 Dart_Precompile(Dart_QualifiedFunctionName entry_points[], bool reset_fields) {
-  UNREACHABLE();
-  return 0;
+  return Api::NewError(
+      "This VM was built without support for AOT compilation.");
 }
 
 
 DART_EXPORT Dart_Handle
 Dart_CreatePrecompiledSnapshotAssembly(uint8_t** assembly_buffer,
                                        intptr_t* assembly_size) {
-  UNREACHABLE();
+  return Api::NewError(
+      "This VM was built without support for AOT compilation.");
   return 0;
 }
 
 
 DART_EXPORT Dart_Handle
 Dart_CreatePrecompiledSnapshotBlob(uint8_t** vm_isolate_snapshot_buffer,
                                    intptr_t* vm_isolate_snapshot_size,
                                    uint8_t** isolate_snapshot_buffer,
                                    intptr_t* isolate_snapshot_size,
                                    uint8_t** instructions_blob_buffer,
                                    intptr_t* instructions_blob_size,
                                    uint8_t** rodata_blob_buffer,
                                    intptr_t* rodata_blob_size) {
-  UNREACHABLE();
-  return 0;
+  return Api::NewError(
+      "This VM was built without support for AOT compilation.");
 }
 
 #else  // DART_PRECOMPILER
 
 DART_EXPORT Dart_Handle
 Dart_Precompile(Dart_QualifiedFunctionName entry_points[], bool reset_fields) {
 #if defined(TARGET_ARCH_IA32)
   return Api::NewError("Precompilation is not supported on IA32.");
 #elif defined(TARGET_ARCH_DBC)
   return Api::NewError("Precompilation is not supported on DBC.");
@@ skipping 234 matching lines @@
 
 DART_EXPORT bool Dart_IsPrecompiledRuntime() {
 #if defined(DART_PRECOMPILED_RUNTIME)
   return true;
 #else
   return false;
 #endif
 }
 
 }  // namespace dart