Removing default build of gcc

[Roman Divacky]

On Fri, Jan 25, 2013 at 02:47:19AM -0600, Mark Linimon wrote:
> On Fri, Jan 25, 2013 at 08:41:11AM +0000, David Chisnall wrote:
> > I think all of the ports that don't build with clang are now explicitly
> > depending on gcc.
> 
> Nope.  We switched some of the most notorious failures, but hundreds
> more remain -- mostly leaf ports.
> 
> Without the ability to run -exp builds, which I do not currently have,
> this is extremely premature.

I also think this is a bit premature, ports is one issue, second one is that
other major archs are still with gcc. Developers should be able to fix 
sources broken on non-clang archs easily.

Once arm/mips/ppc are switched (fingers crossed that it's going to be soon)
disabling gcc by default should be easier.

Roman