Give DwarfPrinter a protected (but not virtual) destructor. Cppcheck

Give DwarfPrinter a protected (but not virtual) destructor.  Cppcheck
warns about this base class not having a virtual destructor, but since
this class has no virtual methods and neither it or the types derived
from it has a destructor, a protected trivial destructor will do (and
shuts cppcheck up) the trick without the cost of introducing a vtable.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@95526 91177308-0d34-0410-b5e6-96231b3b80d8