Start of port to QNX
(Apply commit 5643815)

* include/private/gcconfig.h (I386, OS_TYPE, SA_RESTART, HEURISTIC1,
etext, DATASTART, _end, DATAEND, mach_type_known): Define for QNX.
Update AUTHORS file
Enable prefetch operations by default (GCC 3.0+)

* include/private/gcconfig.h (PREFETCH): Update comment; remove FIXME.
* include/private/gcconfig.h (NO_PREFETCH_FOR_WRITE): Define if
USE_I686_PREFETCH defined but not FORCE_WRITE_PREFETCH.
* include/private/gcconfig.h (PREFETCH, PREFETCH_FOR_WRITE,
CLEAR_DOUBLE): Reformat code (for IA64).
* include/private/gcconfig.h (PREFETCH, PREFETCH_FOR_WRITE): Make
default definition to GCC (v3+) built-in operation for all platforms
(instead of only for Linux/x64) unless NO_PREFETCH (or
NO_PREFETCH_FOR_WRITE, respectively) defined.
Update TODO file (add 1 item about parallel marker)