See #6113 for an alternate way of doing this that we didn't end up
following.
Closes#6079.
I also took the opportunity here to extract C.zig and Elf.zig from
link.zig.
According to the Mach-O file format reference, the first
load command should be a `__PAGEZERO` segment command. The
segment is located at virtual memory location 0, has no protection
rights, and causes acccesses to NULL to immediately crash.
Signed-off-by: Jakub Konka <kubkon@jakubkonka.com>
This commit write out Mach-O header in the linker's `flush`
method. The header currently only populates the magic number,
filetype, and cpu info.
Signed-off-by: Jakub Konka <kubkon@jakubkonka.com>
Exports now have a dirty flag and are rewritten on flush if this flag
has been set.
A couple other minor changes have been made based on Andrew's review.
