ObjFW  Check-in [2ca0e3c7d7]

    $ export OBJCPP="$clang -arch armv7 -E"
    $ export IPHONEOS_DEPLOYMENT_TARGET="9.0"
    $ ./configure --prefix=/usr/local/ios --host=arm64-apple-darwin

  To build for the iOS simulator, use something like this:

    $ clang="clang -isysroot $(xcrun --sdk iphonesimulator --show-sdk-path)"
    $ export OBJC="$clang -arch i386 -arch x86_64"
    $ export OBJCPP="$clang -arch i386 -E"
    $ export OBJC="$clang -arch arm64 -arch x86_64"
    $ export OBJCPP="$clang -arch arm64 -E"
    $ export IPHONEOS_DEPLOYMENT_TARGET="9.0"
    $ ./configure --prefix=/usr/local/iossim --host=x86_64-apple-darwin
    $ ./configure --prefix=/usr/local/iossim --host=arm64-apple-darwin

<h3 id="framework-in-xcode">Using the macOS or iOS framework in Xcode</h3>

  To use the macOS framework in Xcode, you need to add the `.framework`s to
  your project and add the following flags to `Other C Flags`:

    -fconstant-string-class=OFConstantString -fno-constant-cfstrings