Laying some groundwork for rebasing to LLVM trunk

Bunch of fairly-simple API changes to contend with.

Main problem is we're still running into those debuginfo issues.
give up on putting debuginfo in our stdlib, at least for now
Couple more fixes to move around llvm revisions
We're back to the future: rebase to LLVM trunk

Had to improve some of our rewriting; looks like there
must have been an LLVM commit that changes the live-out registers
we see.

Also, temporarily disabled format-checking: the rebase
updated clang-format, which now is formatting a few files
differently.  Will re-enable and re-format in the next commit.
New clang-format results
Note from the llvm-dev list
wip
hacks, but get the dwarf stuff outputting
Get it working again