RFR (M): JDK-8200298 Unify all unix versions of libjsig/jsig.c

[Magnus Ihse Bursie]

When I was about to update jsig.c, I noticed that the four copies for 
aix, linux, macosx and solaris were basically the same, with only small 
differences. Some of the differences were not even well motivated, but 
were likely the result of this code duplication causing the code to diverge.

A better solution is to unify them all into a single unix version, with 
the few platform-specific changes handled on a per-platform basis.

I've made the following notable changes:

* I have removed the version check for Solaris. All other platforms seem 
to do fine without it, and in general, we don't mistrust other JDK 
libraries. An alternative is to add this version check to all other 
platforms instead. If you think this is the correct course of action, 
let me know and I'll fix it.

* Solaris used to have a dynamically allocated sact, instead of a 
statically allocated array as all other platforms have. It's not likely 
to be large, and the size is known at compile time, so there seems to be 
no good reason for this.

* Linux and macosx used a uint32_t/uint64_t instead of sigset_t for 
jvmsigs, as aix and solaris do. This is a less robust solution, and the 
added checks show that it has failed in the past. Now all platforms use 
sigset_t/sigismember().

Also worth noting:

* Solaris is not using pthreads, but it's own thread library, which 
accounts for most of the #ifdef SOLARIS.

* In general, if an implementation was needed on one platform, but has 
no effect or is harmless on others, I've kept it on all platforms 
instead of sprinkling the code with #ifdefs.

To facilitate code review, here is a specially crafted webrev that shows 
the differences compared to each of the individual, original per-OS 
versions of jsig.c:
http://cr.openjdk.java.net/~ihse/JDK-8200298-unify-libjsig/webrev.01

Bug: https://bugs.openjdk.java.net/browse/JDK-8200298
WebRev: http://cr.openjdk.java.net/~ihse/JDK-8200298-unify-libjsig/webrev.03

/Magnus