First of all, if you can stop using JSONKit, you should! Switch to NSJSONSerialization if you can.
But I actually have a very similar issue. I am using cocoa pods to import a dependency that uses JSONKit - so I am stuck with it too! As Mani pointed out, if you want to not build JSONKit for arm64, you need to remove it from the ARCHS build setting. Also, JSONKit no longer builds until you disable the 'isa' error which is just a build setting:
CLANG_WARN_DIRECT_OBJC_ISA_USAGE = NO.
Disabling arm64 and 'isa' errors with cocoapods
For myself, since I used cocoa pods to get JSONKit I needed to change those build settings in my Pods project. I found a blog post on disabling arm64 in cocoa pods, and I modified the code from that post to also disable the 'isa' warning: (this code goes in your Podfile)
# Remove 64-bit build architecture and 'isa' errors from Pods targets
post_install do |installer|
installer.project.targets.each do |target|
target.build_configurations.each do |configuration|
target.build_settings(configuration.name)['ARCHS'] = '$(ARCHS_STANDARD_32_BIT)'
target.build_settings(configuration.name)['CLANG_WARN_DIRECT_OBJC_ISA_USAGE'] = 'NO'
end
end
end