Rework codegen of case ranges

 - Fix multiple issues with the way case ranges were emitted, see test
   cases details about the specific issues.

 - The root issue was not being careful about how basic blocks were
   emitted which led to them being chained together incorrectly,
   resulting in improper control flow.

 - Fixes <rdar://problem/6098585>

llvm-svn: 54006