This adds preliminary support for PowerPC/PowerPC64, for FreeBSD. There are
some issues still:
- Breakpoints don't work well on powerpc64.
- Shared libraries don't yet get loaded for a 32-bit process on powerpc64 host.
- Backtraces don't work. This is due to PowerPC ABI using a backchain pointer in memory, instead of a dedicated frame pointer register for the backchain.
- Breakpoints on functions without debug info may not work correctly for 32-bit powerpc.
Leftover from earlier debugging?