newlib cris: Fix compilation warnings that recent gcc treats as errors

newlib cris: Fix compilation warnings that recent gcc treats as errors

For the newlib part, warnings are all from lack of sync between
libc/machine/cris/sys/signal.h and libc/include/sys/signal.h.  This
commit gets them sufficiently in sync again, functionality-wise and
declaration-wise.  Still, nothing is declared that isn't supported at
the system level (i.e. in libgloss system calls and handled by the
CRIS simulator in the gdb project).