Add QNX to recognized systems

[eleir9268]

We build XNNPACK as a dependency of pytorch mobile and tensorflow lite, see https://github.com/qnx-ports/build-files

For QNX SDP 8.0 it doesn't take many changes for the build to pass.
For QNX SDP 7.1 the build will only work with older versions of XNNPACK (because of missing fp16 / bf16 cpu features).

[google-cla]

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[fbarchard]

Looks good. You'll need to sign the CLA for us to take the change.
I expect there will be little code cleanup things to fix once you can attempt a build.

The cmake file checks for compilers/versions and disabled things like fp16 and bf16, so you may need to tweak the build if you're running into compiler issues