Fix Visual C++ error C2248:

Fix Visual C++ error C2248:
'llvm::TrailingObjects<`anonymous-namespace'::Class1,short,llvm::NoTrailingTypeArg>::additionalSizeToAlloc' :
cannot access protected member declared in class
 'llvm::TrailingObjects<`anonymous-namespace'::Class1,short,llvm::NoTrailingTypeArg>'

 I'm not sure how this compiles with gcc.
 Aren't protecteded members accessible only with protected or public inheritance?

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@244199 91177308-0d34-0410-b5e6-96231b3b80d8