The primary change is to ensure we output a Mach-O file of appropriate
endianness when cross-compiling for an opposite-endian architecture.
Earlier versions of XCode's linker accepted files of either
endianness, reguardless of architecture, but later versions don't,
hence the change.
We use this utility instead of objcopy to embed data into object files
because it offers more control over e.g. section alignment, which is
important for bootimage builds.