fix: vllm serve on Apple silicon

Right now commands like `vllm serve TinyLlama/TinyLlama-1.1B-Chat-v1.0` on
Apple silicon fail with triton errors like these.

```
$ vllm serve TinyLlama/TinyLlama-1.1B-Chat-v1.0
INFO 04-30 09:33:49 [importing.py:17] Triton not installed or not compatible; certain GPU-related functions will not be available.
WARNING 04-30 09:33:49 [importing.py:28] Triton is not installed. Using dummy decorators. Install it via `pip install triton` to enable kernelcompilation.
INFO 04-30 09:33:49 [importing.py:53] Triton module has been replaced with a placeholder.
INFO 04-30 09:33:50 [__init__.py:239] Automatically detected platform cpu.
Traceback (most recent call last):
  File "/Users/dxia/src/github.com/vllm-project/vllm/.venv/bin/vllm", line 5, in <module>
    from vllm.entrypoints.cli.main import main
  File "/Users/dxia/src/github.com/vllm-project/vllm/vllm/entrypoints/cli/main.py", line 7, in <module>
    import vllm.entrypoints.cli.benchmark.main
  File "/Users/dxia/src/github.com/vllm-project/vllm/vllm/entrypoints/cli/benchmark/main.py", line 6, in <module>
    import vllm.entrypoints.cli.benchmark.throughput
  File "/Users/dxia/src/github.com/vllm-project/vllm/vllm/entrypoints/cli/benchmark/throughput.py", line 4, in <module>
    from vllm.benchmarks.throughput import add_cli_args, main
  File "/Users/dxia/src/github.com/vllm-project/vllm/vllm/benchmarks/throughput.py", line 18, in <module>
    from vllm.benchmarks.datasets import (AIMODataset, BurstGPTDataset,
  File "/Users/dxia/src/github.com/vllm-project/vllm/vllm/benchmarks/datasets.py", line 34, in <module>
    from vllm.lora.utils import get_adapter_absolute_path
  File "/Users/dxia/src/github.com/vllm-project/vllm/vllm/lora/utils.py", line 15, in <module>
    from vllm.lora.fully_sharded_layers import (
  File "/Users/dxia/src/github.com/vllm-project/vllm/vllm/lora/fully_sharded_layers.py", line 14, in <module>
    from vllm.lora.layers import (ColumnParallelLinearWithLoRA,
  File "/Users/dxia/src/github.com/vllm-project/vllm/vllm/lora/layers.py", line 29, in <module>
    from vllm.model_executor.layers.logits_processor import LogitsProcessor
  File "/Users/dxia/src/github.com/vllm-project/vllm/vllm/model_executor/layers/logits_processor.py", line 13, in <module>
    from vllm.model_executor.layers.vocab_parallel_embedding import (
  File "/Users/dxia/src/github.com/vllm-project/vllm/vllm/model_executor/layers/vocab_parallel_embedding.py", line 139, in <module>
    @torch.compile(dynamic=True, backend=current_platform.simple_compile_backend)
     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/dxia/src/github.com/vllm-project/vllm/.venv/lib/python3.12/site-packages/torch/__init__.py", line 2543, in fn
    return compile(
           ^^^^^^^^
  File "/Users/dxia/src/github.com/vllm-project/vllm/.venv/lib/python3.12/site-packages/torch/__init__.py", line 2572, in compile
    return torch._dynamo.optimize(
           ^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/dxia/src/github.com/vllm-project/vllm/.venv/lib/python3.12/site-packages/torch/_dynamo/eval_frame.py", line 944, in optimize
    return _optimize(rebuild_ctx, *args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/dxia/src/github.com/vllm-project/vllm/.venv/lib/python3.12/site-packages/torch/_dynamo/eval_frame.py", line 998, in _optimize
    backend = get_compiler_fn(backend)
              ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/dxia/src/github.com/vllm-project/vllm/.venv/lib/python3.12/site-packages/torch/_dynamo/eval_frame.py", line 878, in get_compiler_fn
    from .repro.after_dynamo import wrap_backend_debug
  File "/Users/dxia/src/github.com/vllm-project/vllm/.venv/lib/python3.12/site-packages/torch/_dynamo/repro/after_dynamo.py", line 35, in <module>
    from torch._dynamo.debug_utils import (
  File "/Users/dxia/src/github.com/vllm-project/vllm/.venv/lib/python3.12/site-packages/torch/_dynamo/debug_utils.py", line 44, in <module>
    from torch._dynamo.testing import rand_strided
  File "/Users/dxia/src/github.com/vllm-project/vllm/.venv/lib/python3.12/site-packages/torch/_dynamo/testing.py", line 33, in <module>
    from torch._dynamo.backends.debugging import aot_eager
  File "/Users/dxia/src/github.com/vllm-project/vllm/.venv/lib/python3.12/site-packages/torch/_dynamo/backends/debugging.py", line 35, in <module>
    from functorch.compile import min_cut_rematerialization_partition
  File "/Users/dxia/src/github.com/vllm-project/vllm/.venv/lib/python3.12/site-packages/functorch/compile/__init__.py", line 2, in <module>
    from torch._functorch.aot_autograd import (
  File "/Users/dxia/src/github.com/vllm-project/vllm/.venv/lib/python3.12/site-packages/torch/_functorch/aot_autograd.py", line 26, in <module>
    from torch._inductor.output_code import OutputCode
  File "/Users/dxia/src/github.com/vllm-project/vllm/.venv/lib/python3.12/site-packages/torch/_inductor/output_code.py", line 52, in <module>
    from .runtime.autotune_cache import AutotuneCacheBundler
  File "/Users/dxia/src/github.com/vllm-project/vllm/.venv/lib/python3.12/site-packages/torch/_inductor/runtime/autotune_cache.py", line 23, in <module>
    from .triton_compat import Config
  File "/Users/dxia/src/github.com/vllm-project/vllm/.venv/lib/python3.12/site-packages/torch/_inductor/runtime/triton_compat.py", line 16, in <module>
    from triton import Config
ImportError: cannot import name 'Config' from 'triton' (unknown location)
```

We cannot install `triton` on Apple silicon because there are no [available
distributions][1].

This change adds more placeholders for triton modules and classes that are
imported when calling `vllm serve`.

[1]: https://pypi.org/project/triton/#files

Signed-off-by: David Xia <david@davidxia.com>

Author: davidxia

vllm/triton_utils/importing.py

@@ -2,6 +2,7 @@
 
 import sys
 import types
+from abc import ABC
 from importlib.util import find_spec
 
 from vllm.logger import init_logger
@@ -25,6 +26,8 @@ def __init__(self):
             self.autotune = self._dummy_decorator("autotune")
             self.heuristics = self._dummy_decorator("heuristics")
             self.language = TritonLanguagePlaceholder()
+            self.Config = self._dummy_decorator("Config")
+            self.__version__ = ""
             logger.warning_once(
                 "Triton is not installed. Using dummy decorators. "
                 "Install it via `pip install triton` to enable kernel"
@@ -43,11 +46,36 @@ class TritonLanguagePlaceholder(types.ModuleType):
 
         def __init__(self):
             super().__init__("triton.language")
-            self.constexpr = None
+            self.constexpr = lambda x: x
             self.dtype = None
+            self.extra = None
+            self.math = None
+            self.tensor = None
+
+    class TritonCompilerPlaceholder(types.ModuleType):
+
+        def __init__(self):
+            super().__init__("triton.compiler")
+            self.CompiledKernel = ABC
+
+    class TritonRuntimeAutotunerPlaceholder(types.ModuleType):
+
+        def __init__(self):
+            super().__init__("triton.runtime.autotuner")
+            self.OutOfResources = ABC
+
+    class TritonRuntimeJitPlaceholder(types.ModuleType):
+
+        def __init__(self):
+            super().__init__("triton.runtime.jit")
+            self.KernelInterface = ABC
 
     sys.modules['triton'] = TritonPlaceholder()
     sys.modules['triton.language'] = TritonLanguagePlaceholder()
+    sys.modules['triton.compiler'] = TritonCompilerPlaceholder()
+    sys.modules[
+        'triton.runtime.autotuner'] = TritonRuntimeAutotunerPlaceholder()
+    sys.modules['triton.runtime.jit'] = TritonRuntimeJitPlaceholder()
 
 if 'triton' in sys.modules:
     logger.info("Triton module has been replaced with a placeholder.")