It's pointless if we argue about the interpretations of terms. What's clear to me is that OpenSolaris isn't just the kernel.

I didn't recommend Schillix to this thread's poster because OpenSolaris isn't that easily compatible with Solaris.

1- They use a version of gcc that's not the same with Solaris < 10

2- There are newer libraries and headers beginning with Solaris 10. (As an example, <stdint.h> isn't present in Solaris 9 (SunOS 5.9).

So compiling on OpenSolaris isn't a guarantee that they'll compile on Solaris 5.6~8 which is still used in many universities.

I still test my software for portability on true solaris servers. I can't still use Schillix for this purpose.

I fully agree with you on both.
It is more compatible than anything not Solaris.

This has nothing to do with Solaris, same can be said from on Linux distro to another.
Anyway, the preferred compiler on Solaris is Sun C compiler, not gcc.

Good point, but the OP didn't mentioned which Solaris version was targeted.
Moreover, he mentioned Posix as being the goal, and stdint.h is a new specification arriving with C99.
Perhaps being C99 compliant is the OP goal, in that case Solaris 10+ is a better option than Solaris 9-.

I don't want to argue again about vocabulary, but do you mean Solaris 10 is not a true server ?