Add external definitions for commonly-used template specializations and add

Add external definitions for commonly-used template specializations and add
anchor methods to others.  This eliminates the vtable/template method bloat
in .o files that defining a cl::opt used to impose (~4K per .o file for one
cp::opt<unsigned>).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@29909 91177308-0d34-0410-b5e6-96231b3b80d8