FYI: libc syscall stubs are out-of-date w.r.t the new signal code.  We
need sig*14 syscall stubs in libc, plus, I guess, a RENAME() trick and
library wrapper code that emulates the old signal-delivery API using
the new sig*14 stubs.

Right now, we don't appear to have the new stubs, and a libc build
fails trying to build the old stubs (since the old SYS_sig* names
aren't defined in syscall.h anymore).

(I expect this is part of the "falllout" Jason referre to yesterday)