Remove support for unsupported MSVC versions

Re-land r367727 with the #if fixed.

Reviewers: rnk, lebedev.ri

Subscribers: hiraditya, jkorous, dexonsmith, lebedev.ri, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D65662

llvm-svn: 367734