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
one new .cpp file, in preparation for merging in the Direct Object Emission
changes we're working on. No functional changes.
Fixed coding style issues on the original patch. Patch by Aaron Gray
llvm-svn: 72754
