0.8.19.1: PowerPC linkage tables (darwin only for now)
* Linkage tables are now implemented on PowerPC.
Right now I've only enabled it on Darwin; to enable it on Linux,
the addresses used for linkage table spaces would need to be tested.
* Lazy foreign functions do not work correctly - the code expects the signal
that occurs when jumping to a write-protected page to be the same as the
signal that occurs when reading from one. On Darwin the former is SIGBUS
and the latter is SIGSEGV; this means that the fault address testing does
not work on Darwin.