macho: implement -search_paths_first and -search_dylibs_first

[motiejus]

Ignore MachO-specific flag -search_paths_first, since it is the default
in zld and ld64.

Also see Jakub's comment1:

Changing topic slightly, @motiejus dunno if you noticed, with this
change building arm64 Zig binary fails on macos - it complains about
unknown -search_paths_first flag. This one is an easy fix: we should
ignore it since this is the default behaviour in both ld64 and zld.

[kubkon]

Thanks for the PR @motiejus! I'm going to hijack your branch and fix another unhandled flag -headerpad_max_install_names, and push all in one go. However, before this happens, I wanna land #11910 first so that I can immediately add some relevant linker tests. Hope you don't mind!

[kubkon]

Apologies for making you a reviewer on your own PR @motiejus, but would you mind having a look? Instead of implementing -headerpad_max_install_names, I've decided to implement -search_dylibs_first which is another possible search strategy to -search_paths_first in MachO linkers. I've also noticed we were substituting a static archive (if found) for a system library name (i.e., -la was getting transformed into <path>/liba.a in main.zig). This is actually wrong targeting MachO as we want to defer the resolution of all libs to the link stage so that we can correctly act on the -search_paths_first and -search_dylibs_first flags.

[motiejus]

Apologies for making you a reviewer on your own PR @motiejus, but would you mind having a look?

Sure! Sorry for not reviewing earlier; you posted this on the day of summer solstice :)