... I browsed the web the other day and became a deep urge to compile some C code... , so as I was on Mac OS, I didn't have any C compiler really handy. That, for what it's worth, brought me here.
If we are talking strictly about the kernel, I doubt its that heavily modified (more stripped down to what they need). The argument for the BSD license seems to be that people should be free to not disclose there source code... but why anyone would want to work for free to help Microsoft and Apple make a profit off of it by making it proprietary is beyond me!
gcc is available for mac, you can compile it yourself quite easily actually. Hard to say which license ultimately allows the most freedom. The licence using copyleft to impose restricions to allow freedom, or the one which allows all freedom anyway.
Depends which way you look at freedom... The GPL gives you the right to demand source code if they have not already provided it. If you want to keep your source code closed then you can't sell or give your software to anyone else / use it outside your company. The BSD license gives you the right to deny the rights that you were granted (to use the source code that you have found) to everyone else if you distribute your work. Which is more free? depends if your trying to make a profit from it (as opposed to making a profit using it, aka MySQL, which you can do easily with ether license).
I use GCC on my Mac, I installed it as part of the developer account I have with them I believe. Works like a charm.