parse

        fn parse(arch: Target.Cpu.Arch, reader: *Io.Reader) !?Target.Cpu {
            var obj: impl = .{};
            while (try reader.takeDelimiter('\n')) |line| {
                const colon_pos = mem.findScalar(u8, line, ':') orelse continue;
                const key = mem.trimEnd(u8, line[0..colon_pos], " \t");
                const value = mem.trimStart(u8, line[colon_pos + 1 ..], " \t");
                if (!try obj.line_hook(key, value)) break;
            }
            return obj.finalize(arch);
        }