MS static locals mangling: don't count enum scopes

We may not have the mangling for static locals vs. enums completely figured out,
but at least for my simple test cases, enums should not increment the mangling
number.

Differential Revision: http://reviews.llvm.org/D4164

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@211078 91177308-0d34-0410-b5e6-96231b3b80d8