How to disable CLANG & co build in buildworld?

[M. Warner Losh]

In message: <20100611203544.GA1797 at hoeg.nl>
            Ed Schouten <ed at 80386.nl> writes:
: It should be noted that tblgen is not the only tool that may get built
: for nothing. Another example is aicasm, which is always built, even if
: ahc is not placed in the kernel configuration file.

That's another one I'd like to fix :)  But it only takes seconds to
build...

Warner