clang isn't working after all

Not sure how I didn't notice before, but qemu core dumps when I try and
load the OS in qemu. So I'm removing the instructions for building with
it until I get it working.
Fixed clang and made it the default

I had changed the linker invocation to use clang so that people might be
able to get away without building anything. Without realizing that clang
just forwards linking onto the system ld, which is wrong for us. So I
changed the last line to directly invoke i686-elf-ld (hopefully
correctly) and clang now works again. I thought it worked before...
Eventually I'll learn to stop playing games with git. (Or at least I'll
learn what games are better left unplayed).