Removed hardcoded -arch x86_64 for MacOS nifs

[dominicletz]

Just checked git blame and this flag seems to have been there from the very beginning (powerpc remenant?). For current macs the flag seems problematic as it overrides the default choice of building for the current architecture and hence prevents building on ARM based macs.

[dominicletz]

Another thought on this: Even more convenient might be a check for the arch of the OTP system in $PATH to ensure the resulting NIFs are always compatible with that. E.g. with Rosetta2 an ARM user can install and use an intel based OTP build, and might even use that for building. -- Not sure though atm how to best get the right arch flags from erl...

[essen]

But would that be a common scenario? If not, don't worry about it for now. I'll try to get to your PRs soon but I am crunching on something at the moment so it might take a week or two.

[essen]

I will get to this when I am back at work. @lhoguin

[essen]

Merged, thanks!