Support producer mode on Apple Silicon

[polac24]

PLATFORM_PREFERRED_ARCHbuild setting is still resolved to x86_64 on M1 machines (see a report here). The aim of using PLATFORM_PREFERRED_ARCH was to find a default architecture to build.

PLATFORM_PREFERRED_ARCH values:

For Intel machines, it is:

• building for simulator -> x86_64
• building for device -> 'arm64'

For Apple silicon machines, it is:

• building for simulator -> x86_64
• building for device -> 'arm64'

Solution

Instead, we can recognize the architecture from the ARCHS env. For a default Debug configuration, it always resolves to a single architecture. If "Build Archive Architecture Only" is disabled (not recommended), we can just the first one.

ARCHS values:

For Intel machines, it is:

• building for simulator -> x86_64
• building for device -> arm64

For Apple silicon machines, it is:

• building for simulator -> arm64
• building for device -> arm64

when ONLY_ACTIVE_ARCH=NO

For Intel machines, it is:

• building for simulator -> arm64 x86_64
• building for device -> arm64

For Apple silicon machines, it is:

• building for simulator -> arm64 x86_64
• building for device -> arm64

Fixes #33

[imWildCat]

Thanks a lot!