[Chore] Add arm64 as valid arch when building for simulator on M1 macs

[michaelknoch]

this pr allows building and linking Down when running on arm64 simulator

Error message without this:

Could not find module 'Down' for target 'arm64-apple-ios-simulator'; found: x86_64-apple-ios-simulator, x86_64

[michaelknoch]

@johnxnguyen

[johnxnguyen]

Hey @michaelknoch , thanks for the contribution! Do you know if a similar solution is needed when Down is pulled in via Swift Package Manager?

[michaelknoch]

I think exactly this change is needed when fetching Down via SPM for running an ios application on an arm64 simulator, but I haven't tried it. We are fetching Down as a git submodule and embedding it directly into the xcode project. I was wondering if it would make sense to get rid of the VALID_ARCHS variable entirely. Xcode should be able to set the ARCHS variable (which is basically the same) automatically. @johnxnguyen

[johnxnguyen]

I was wondering if it would make sense to get rid of the VALID_ARCHS variable entirely. Xcode should be able to set the ARCHS variable (which is basically the same) automatically.

@michaelknoch unfortunately I don't have an M1 laptop so can't really say what works or doesn't work. If this PR solves the issue for you, I'm happy to to approve it.

[michaelknoch]

It does definitely solve the build errors when building for an arm64 simulator on an M1 mac @johnxnguyen

[johnxnguyen]

Thanks again @michaelknoch