Absolute addressing through constant with Apple's cc
* kern/i386/pc/startup.S: Define necessary constants
and address through it when using ABS with Apple's CC
* boot/i386/pc/diskboot.S: likewise
* boot/i386/pc/boot.S: likewise
* boot/i386/pc/lnxboot.S: likewise
* boot/i386/pc/cdboot.S: likewise
* mmap/i386/pc/mmap_helper.S: likewise
* commands/i386/pc/drivemap_int13h.S: likewise