[sanitizer] Transition from _zx_vmar_... to _zx_vmar_..._old calls

This is a preparation for breaking changes to _zx_vmar_... calls.
We will transition back to _zx_vmar_... after all the changes to
these symbols are done and become part of the Fuchsia SDK.

Differential Revision: https://reviews.llvm.org/D49697

llvm-svn: 337801