This adds location info for all llvm_unreachable calls (which is a macro now) in
!NDEBUG builds.
In NDEBUG builds location info and the message is off (it only prints
"UREACHABLE executed").

llvm-svn: 75640

Make llvm_unreachable take an optional string, thus moving the cerr<< out of
line.
LLVM_UNREACHABLE is now a simple wrapper that makes the message go away for
NDEBUG builds.

llvm-svn: 75379

llvm-svn: 73464

llvm-svn: 72948

logical/sane approach to organizing all of the stuff that goes into writing out
DWARF information. Honestly? even this is too complex for what it's supposed to
be doing.

Trivia: It *looks* like there would be functionality changes, however there aren't!
llvm-svn: 71821