update setup.py to allow "wheel" construction on mac

[andy-neuma]

SUMMARY:
allows "wheel" generation on macOS. reuses the ENV, NM_ALLOW_DARWIN.

TEST:
checks after the updating the condition.

❯ export NM_ALLOW_DARWIN=0
❯ python3 setup.py sdist bdist_wheel
Loaded version 1.6.0 from /Users/andy/sidelot/wand/deepsparse/src/deepsparse/generated_version.py
Traceback (most recent call last):
  File "/Users/andy/sidelot/wand/deepsparse/setup.py", line 223, in <module>
    _check_supported_system()
  File "/Users/andy/sidelot/wand/deepsparse/setup.py", line 188, in _check_supported_system
    raise OSError(
OSError: Native Mac is currently unsupported for DeepSparse. Please run on a Linux system or within a Linux container on Mac. More info can be found in our docs here: https://docs.neuralmagic.com/deepsparse/source/hardware.html

and enabling it

❯ export NM_ALLOW_DARWIN=1
❯ python3 setup.py sdist bdist_wheel
Loaded version 1.6.0 from /Users/andy/sidelot/wand/deepsparse/src/deepsparse/generated_version.py
Checking to see if /Users/andy/sidelot/wand/deepsparse/src/deepsparse/arch.bin exists.. True
running sdist
running egg_info
...
adding 'deepsparse_nightly-1.6.0.dist-info/top_level.txt'
adding 'deepsparse_nightly-1.6.0.dist-info/RECORD'
removing build/bdist.macosx-10.9-universal2/wheel

[bfineran]

LGTM pending @dbarbuzzi's comment

[bfineran]

looks good to me, we should probably just add a helper across our repos to evaluate truthy values from environment variables