Defines starting with `b' in osfmk/i386/AT386

• BOOT_LINE_LENGTH osfmk/i386/AT386/model_dep.c:147
• BOOT_STRING_LEN osfmk/i386/AT386/kernBootStruct.h:134
• BOOT_TO_VIRT osfmk/i386/AT386/asm_startup.h:223