Add Solaris support (#3515)

I love jq :) So while updating the version we ship in Solaris I have
tried to modify stuff to make everything work out of the box. Just

```
autoreconf -fiv
./configure
gmake
gmake check
```

I also went ahead and created Solaris test action should you be
interested in having it too. The changes are not extensive and I have
tried to comment them nicely in each commit. Hopefully that's enough.

Thanks for jq!