MS ABI: Stick internal vftables in a comdat if they have RTTI data
Previously, we would have a private backing variable and an internal
alias pointing at it.
However, -fdata-sections only fires if a global variable has non-private
linkage. This means that an unreferenced vftable wouldn't get
discarded, bloating the object file.
Instead, stick the backing variable in a comdat even if the alias has
internal linkage. This will allow the linker to drop the vftable if it
is unused.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@212901
91177308-0d34-0410-b5e6-
96231b3b80d8