Removing default build of gcc

[Mark Linimon]

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.

mcl