Fix architecture detection on MacOS to be configuration-cache friendly

[msridhar]

See diffplug/goomph#211. Executing uname -a causes configuration cache issues, so get the info from the os.arch system property instead.

[nedtwigg]

Thanks for the PR! On an M1 mac, you can use the arch command to run something under x86 or arm. On an M1 mac, It should be that

• OS.getRunning() will report either arm or x86 based on whether you are using the x86 Rosetta emulation or the native ARM exection
• OS.getNative() should always return arm

These requirements are definitely met by uname. I think they are not met by os.arch, though I might be wrong. Do you have access to an M1 or M2 mac? If so, can you:

• use arch to setup a case with the existing published version that says OS.getRunning is x86 and OS.getNaive is arm
• repeat that test with the change proposed in this PR

If you report that this works, I'm happy to merge and release it.

[msridhar]

Thanks for the feedback! I don't think this PR will work according the requirements. In particular when running under Rosetta I think getNative() will return x86 incorrectly. So I think a different approach is needed. Shall I go ahead and close this PR?