- Add a "getOrInsertGlobal" method to the Module class. This acts similarly to

  "getOrInsertFunction" in that it either adds a new declaration of the global
  and returns it, or returns the current one -- optionally casting it to the
  correct type.
- Use the new getOrInsertGlobal in the stack protector code.
- Use "splitBasicBlock" in the stack protector code.

llvm-svn: 58727