在ubuntu下编译Android5.1源码，报错。，怎么解决

external/libcxx/include/atomic:539:2: error: #error is not implemented
art/runtime/atomic.h:155:5: error: 'atomic_thread_fence' is not a member of 'std'
art/runtime/atomic.h:155:30: error: 'memory_order_acquire' is not a member of 'std'
art/runtime/entrypoints/entrypoint_utils.h:50:44: error: 'art::mirror::Class* art::CheckClassInitializedForObjectAlloc(art::mirror::Class*, art::Thread*, bool*)' declared 'static' but never defined [-Werror=unused-function]
art/runtime/entrypoints/entrypoint_utils.h:146:33: error: 'art::mirror::ArtField* art::FindFieldFast(uint32_t, art::mirror::ArtMethod*, art::FindFieldType, size_t)' declared 'static' but never defined [-Werror=unused-function]
art/runtime/entrypoints/entrypoint_utils.h:152:34: error: 'art::mirror::ArtMethod* art::FindMethodFast(uint32_t, art::mirror::Object*, art::mirror::ArtMethod*, bool, art::InvokeType)' declared 'static' but never defined [-Werror=unused-function]
art/runtime/entrypoints/entrypoint_utils.h:158:30: error: 'art::mirror::Class* art::ResolveVerifyAndClinit(uint32_t, art::mirror::ArtMethod*, art::Thread*, bool, bool)' declared 'static' but never defined [-Werror=unused-function]
art/runtime/entrypoints/entrypoint_utils.h:166:31: error: 'art::mirror::String* art::ResolveStringFromCode(art::mirror::ArtMethod*, uint32_t)' declared 'static' but never defined [-Werror=unused-function]