This is used for two purposes:
1. Use the new legacy icon when targeting 10.5 or older. This fixes
bug #11261 MAC OS X: App icon doesn’t display on OS X 10.5.8.
2. Do not attempt to compile the dock plugin in 32 bits when
targeting 10.14 or newer. This fixes the bundle target as support
for compiling 32 bits binaries was removed in SDK 10.14.
This commit also removes the bundle64 target as it is no longer
needed.
