ms-inline-asm: Add a test to ensure that call doesn't clobber eax.

Note that it's not clear whether this is the right behavior, please see
the review for the discussion.

Reviewers: rnk

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D4577

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@214401 91177308-0d34-0410-b5e6-96231b3b80d8