Peter Naulls <peter@chocky.org>. r=wtc.
Modified files: configure configure.in _pth.h prosdep.h prlink.c
prmem.c unix.c uxrng.c prsystem.c ptio.c ptthread.c
Added files: _riscos.cfg _riscos.h riscos.c
git-svn-id: svn://10.0.0.236/trunk@175501 18797224-902f-48f8-a5cc-f745e15eee43