Quite a while ago, the sig_atomic_t type was moved from <sys/signal.h>
to <machine/signal.h>.  

This is not a problem, except when compiling with _ANSI_SOURCE
defined, because <machine/signal.h> is not #included then. 

There are several ways we can fix this problem: one is to add an
_ANSI_SOURCE conditional to <machine/signal.h> to remove the
sigcontext stuff, or we could make the type of sig_atomic machine
independant.  Since sig_atomic_t is defined as "typedef int
sig_atomic_t" for all arch's, there is no need to make it machine
dependant.

I'm currently favouring the first approach.  Any objections?

	--jtc