This re-applies D5195: Add a RTS option -xp to load PIC object anywhere in address space with fixes for i386:
- Fix unused label warnings, see D5230: rts/Linker.c: define the 'mmap_again' label only for x86_64 or D5273: Fix unused label on non x86_64 platforms
- Fix a silly bug introduced by moving #if
Add a RTS option -xp to load PIC object anywhere in address space. We do
this by relaxing the requirement of <0x80000000 result of
mmapForLinker and implying USE_CONTIGUOUS_MMAP.
We also need to change calls to ocInit and ocGetNames to avoid
dangling pointers when the address of oc->image is changed by