[MS ABI] Fix mangling issue with dynamic initializer stubs.
There are two types of dynamic initializer stubs. There's
`dynamic initializer for 'x''(void)
and
`dynamic initializer for `static Foo::Bar StaticDataMember''(void)
The second case is disambiguated from the first by the presence of
a ? after the operator code. So the first will appear something like
?__E<name> while the second will appear something like ?__E?<name>.
clang-cl was mangling these both the same though. This patch
matches behavior with cl.
Differential Revision: https://reviews.llvm.org/D51500
llvm-svn: 341117