[FLAG DAY] once 16344 is on your build machine, your source trees must match

[FLAG DAY] once 16344 is on your build machine, your source trees must match

[Richard Lowe]

If you don't maintain a machine used to build illumos, you can ignore me.

The integration of:
    16344 -Wstrict-prototypes warnings about SIG_DFL, SIG_ERR, SIG_IGN
and SIG_HOLD signal constants

constitutes a minor flag day whereby, once your build machine has this change
builds of illumos from before this change will fail.

This is because the native SMF tools are (correctly) built against the system
headers and, once you have the fixed signal.h, the compilers will notice that
the native SMF tools are incorrect.

The easiest way to fix this is just to not build old software on new releases,
or to backport this change into that old software.

You may also have similar trivial problems with software you added
to illumos-gate downstream.

Issues fall into a handful of basic groups:

- Assigning to the wrong one of `sa_handler` v. `sa_sigaction` in
`struct sigaction`.
- Declaring signal(3C) style signal handlers incorrectly (they take an integer
  argument)
- Slightly more complicated but less likely, attempting to define a generic
  type for "signal handling function", even though this can't be expressed
  (see the diffs in this change for mdb and syseventd).
-- Rich