Enable CPU-only builds on macOS

[tilmantroester]

This PR enables CPU-only builds on macOS. It in addition to the changes to spconv, this also requires some changes to ccimport and cumm. They are implemented at https://github.com/tilmantroester/ccimport/tree/macos_support and
https://github.com/tilmantroester/cumm/tree/macos_cpu_only. Let me know if you want PRs for those as well.

I've tested this on an arm64 mac, with both Apple and conda clang.
For development installs (pip install -e), both JIT and non-JIT work. Standard installs require the non-JIT build.

Compiling with OpenMP works but the results are unstable, so I disabled OpenMP on macOS.

tests/test_conv.py passes for the cases where CPU implementations are available (i.e. ConvAlgo.Native but not for example SparseGlobalMaxPool).

[xiaohuang2004]

Hello, thank you for contribution to macOS. I saw your branch for ccimport and cumm. I try to install ccimport, cumm and spconv.(I git clone all them and then use pip install -e . to install them.) Then I try to run tests/test_conv.py. Unfortunately, it seems that something is wrong in cumm.
Traceback (most recent call last): File "/Users/apple/Desktop/spconv/spconv/test/test_conv.py", line 28, in <module> from spconv.core import ConvAlgo File "/Users/apple/Desktop/spconv/spconv/spconv/__init__.py", line 15, in <module> from . import build as _build File "/Users/apple/Desktop/spconv/spconv/spconv/build.py", line 21, in <module> from .constants import PACKAGE_NAME, PACKAGE_ROOT, DISABLE_JIT, SPCONV_INT8_DEBUG File "/Users/apple/Desktop/spconv/spconv/spconv/constants.py", line 19, in <module> from cumm.gemm.constants import NVRTCMode File "/Users/apple/Desktop/spconv/cumm/cumm/__init__.py", line 28, in <module> pccm.builder.build_pybind([ArrayPtr(), TensorViewBind()], File "/opt/anaconda3/envs/spconv/lib/python3.10/site-packages/pccm/core/__init__.py", line 983, in wrapper func(self, *args, **kwargs) File "/Users/apple/Desktop/spconv/cumm/cumm/tensorview_bind.py", line 51, in __init__ cuda_ver = get_cuda_version_by_nvcc().split(".") File "/Users/apple/Desktop/spconv/cumm/cumm/common.py", line 224, in get_cuda_version_by_nvcc nvcc_version = subprocess.check_output(["nvcc", "--version" File "/opt/anaconda3/envs/spconv/lib/python3.10/subprocess.py", line 421, in check_output return run(*popenargs, stdout=PIPE, timeout=timeout, check=True, File "/opt/anaconda3/envs/spconv/lib/python3.10/subprocess.py", line 503, in run with Popen(*popenargs, **kwargs) as process: File "/opt/anaconda3/envs/spconv/lib/python3.10/subprocess.py", line 971, in __init__ self._execute_child(args, executable, preexec_fn, close_fds, File "/opt/anaconda3/envs/spconv/lib/python3.10/subprocess.py", line 1863, in _execute_child raise child_exception_type(errno_num, err_msg, err_filename) FileNotFoundError: [Errno 2] No such file or directory: 'nvcc'