Add sigaltstack() prototype - Round 2

[Joel Sherrill <joel dot sherrill at oarcorp dot com>]

Hi

The RTEMS Project has been porting more and more FreeBSD code
for capabilities like IPV6, USB, and user level commands. We are
trying very hard not to have to modify the source code as we
move it over. Some of the kernel code we have brought over
resulted in this needing to be added.

I first proposed v1 of this patch 2 years ago and dropped it.
I attempted address those comments though. See the other
recent thread.

This method is defined here:

http://pubs.opengroup.org/onlinepubs/009695399/functions/sigaltstack.html

One odd thing is that newlib uses <sys/signal.h> for <signal.h> prototypes
so I followed the pattern.   Not much really to the patch. It adds:

+ typedef struct  sigaltstack {...} stack_t
+ sigaltstack() prototype protected

The big question (as always) is whether or not the guards on the methods
are correct.

2014-08-15 Joel Sherrill <joel.sherrill@oarcorp.com>

    * libc/include/sys/signal.h: Add sigaltstack() support.


-- 
Joel Sherrill, Ph.D.             Director of Research & Development
joel.sherrill@OARcorp.com        On-Line Applications Research
Ask me about RTEMS: a free RTOS  Huntsville AL 35805
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