Move llvm/Support/IRBuilder.h -> llvm/IRBuilder.h

This was always part of the VMCore library out of necessity -- it deals
entirely in the IR. The .cpp file in fact was already part of the VMCore
library. This is just a mechanical move.

I've tried to go through and re-apply the coding standard's preferred
header sort, but at 40-ish files, I may have gotten some wrong. Please
let me know if so.

I'll be committing the corresponding updates to Clang and Polly, and
Duncan has DragonEgg.

Thanks to Bill and Eric for giving the green light for this bit of cleanup.

llvm-svn: 159421