zld: ignore -search_paths_first

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

Also see Jakub's comment[1]:

    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.

[1]: ziglang#11906 (comment)

src/main.zig

@@ -1475,6 +1475,8 @@ fn buildOutputType(
                                 mem.eql(u8, linker_arg, "-static"))
                             {
                                 force_static_libs = true;
+                            } else if (mem.eql(u8, linker_arg, "-search_paths_first")) {
+                                // ignore, since it's the default behavior in both ld64 and zld
                             } else {
                                 try linker_args.append(linker_arg);
                             }