Add support for the arm64 architecture for macOS

[dsanghan]

Verified with:

> lipo -archs jre_emul/build_result/macosx/libjre_emul.a 
x86_64 arm64

Is anything else needed?

[dsanghan]

make dist completes correctly, but make frameworks outputs an error:
Both macos-arm64 and macos-x86_64 represent two equivalent library definitions.

From the forums it seems we're supposed to use lipo for this - so use build_result/macosx/lib instead of build_results/objs_/lib - but not sure how to do that

[dsanghan]

That does seem to work - making the above change does generate a xcframework but involves modifying the gen_frameworks script to use the fat lib with 2 archs instead of the static lib:

[tomball]

Unfortunately xcodebuild -create-framework fails because it considers macos-x86_64 and macos-arm64 to "represent two equivalent definitions." This Apple Developer Forum discussion has the fix.

Adding a lipo step to some of the framework slices involves more Make hackery than just adding a new architecture. Do you want to give it a shot, or should I add it in a follow-up commit?

[dsanghan]

Would be great if you could add a follow-up commit

[tomball]

LGTM -- thanks!