Steps to reproduce:

1. Open attached 'test-lib-2019.zip' project (or open an empty project and install 'Burst' package via Package Manager)
2. Switch build target to iOS and make a build
3. Open the project in Xcode 12
4. Make sure that the Xcode project is using the "New Build System" (File/Project Settings/Build System)
5. Try to build the project

Expected result: build succeeds
Actual result: build fails with "The linked library 'lib_burst_generated32.a' is missing one or more architectures required by this target: arm64"

Notes:
This does not happen when building an ARM64-only build, therefore it's not reproducible on 2020.1+ (ARMv7/Universal architectures were removed there)
Doesn't fail on Xcode 11

Reproduced with: 2018.427f1, 2019.4.11f1