...the mangled names of the corresponding symbols change with MSVC if you change
a member from public to protected.  This had been changed with
6e67c03d "Enable -Wnon-virtual-dtor for GCC 4.6"
but should only be necessary for GCC, not for MSVC, so can simply be reverted
under _MSC_VER.

Change-Id: Id22aadaff3d7f30ed824f39fe22eab7ca39bd408