I just ran into an interestig problem with perl.  After fixing strtod
lossage in my toolchain, perl built OK, but failed a half-dozen tests
involving signalsp when I ran `make test

Turns out perl's util.c pulls in <sys/signal.h>, but does **not**
#include <signal.h>, since NSIG is already defined (from
<sys/signal.h>).

So perl';s signal-handling code ends up getting struct sigcontext from
sys/signal.h, but none of the _RENAME stuff. So perl calls the old
sigaction() with a new-style sigcontext. Which, not surprisingly, loses.

I dunno how we handle this.  For now  I've dinked util.c to do
  #include  <signal.h> 

on NetBSD, even if NSIG is defined. (just add !defiend(__NetBSD__) to
the list of exceptions).  But I wonder what other third-party code is
silently failing. Should we do

     #ifndef _KERNEL
     #include <signal.h>
     #endif

in sys/signal.h, to avoid this?  Does that conflict with POSIX?
What about other _RENAMES?