[PATCH] rename _LIBCPP_TYPE_VIS_ONLY to _LIBCPP_TEMPLATE_VIS

[Reid Kleckner]

I don't think we should be using this linkage on non-template types, even if Howard thought they were "header only".  Even those tag types can be exported from libc++.  If someone takes the address of a tag or once_flag assignment operator, libc++ should have a definition of it.  Marking it as dllexport (aka _LIBCPP_TYPE_VISIBILITY) makes that work.

On the other hand, we have things like struct nullptr_t, which are never compiled while building libc++ itself.  Saleem has moved to give them no decoration, which means each DSO would get its own set of member functions with distinct addresses.

The upshot is I think we should go forward with this change.  This attribute really shouldn't be applied to non-template types, despite what Howard said in the past.

http://reviews.llvm.org/D4530