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?
 

llvm-svn: 244199