Make debugging information usable. This is barebones, but it makes -g

actually work (instead of crashing llc), and there's enough info emitted 
to get line number information in gdb. This should hopefully be helpful 
for debugging non-working programs.

I got rid of the begin/endregion calls because the implementation wasn't 
working; someone who knows the debugging info a bit better might try to 
add it. I really have no clue how a compiler is supposed to emit them.

This commit shouldn't have any effect without -g.

llvm-svn: 51404