[PATCH] fix a leak in CodeGenFunction::EmitSwitchStmt (detected by lsan)

[Kostya Serebryany]

  Placing OwningPtr inside JumpDest would be much more involved.
  One reason is that JumpDest objects are copied around and JumpDest's copy CTOR is banned (LLVM_DELETED_FUNCTION).

http://llvm-reviews.chandlerc.com/D2472