Disable OpenMP during OSX/Windows wheel building

[djhoese]

@rayg-ssec noticed that the newest wheels have OpenMP in them and are therefore broken on most systems. Let's see how quick I can disable this.

[rayg-ssec]

Further details for posterity:

• the pykdtree 1.3.7 py311 prebuilt wheel for arm64 fails to load due to missing symbol ___kmpc_for_static_fini which is, as I understand it, part of libomp
• the otool -L output on the .so universal binary in the wheel is linked to /usr/local/opt/libomp/lib/libomp.dylib on its x86-64 code and not on arm64 code. This looks like homebrew is in play.
• @djhoese confirmed that the probe logic was identifying a homebrew install of libomp, and that the build was getting warnings about it not being a universal dylib.
• pip installs where it resorts to source instead of prebuilt wheel run through test_tree.py fine.

As a result, the binary wheel might work for intel macOS with homebrew libomp installed - though homebrew has at least one configuration where libomp is only provided as static (libomp.a).

The two main solutions as I see it are

• reconfigure homebrew on build system to provide a universal libomp.a
• set USE_OMP=0 on at least macOS, or, equivalently, use a build system without homebrew

[djhoese]

Thanks @rayg-ssec. It may be worth playing with https://github.com/pypa/auditwheel and see what it says. We use this in the scripts/build-manylinux-wheels.sh script in pykdtree.

[djhoese]

Oh nevermind, auditwheel is Linux only.

[djhoese]

Latest commit shows:

 OpenMP support not available.
Compiler: unix / OpenMP: None / OpenMP compile args: [] / OpenMP link args: []

For OSX and Windows so I think we're back to normal there.