I get an immediate crash when trying to compile the current JUCE git tree for iOS 64 bit. It compiles ok for iOS 32 bit.
My compile flags are: -arch arm64 -mtune=native -fPIC -miphoneos-version-min=7.0
The clang version is Apple LLVM version 7.0.0 (clang-700.0.72)
Just to mention: 64-bit support is now required for iOS apps in the App Store.