ms-inline-asm: Add a test case for the usage of labels in bracket expressions

Summary: This is a test for this patch: http://reviews.llvm.org/D5445.

Reviewers: rnk

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D5446

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@218271 91177308-0d34-0410-b5e6-96231b3b80d8