[ms-cxxabi] Mangle dynamic initializer stubs the same way MSVC does

Summary: Dynamic initializers are mangled as ??__E <name> YAXXZ.

Reviewers: timurrrr

CC: cfe-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D1477

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@190434 91177308-0d34-0410-b5e6-96231b3b80d8