Remove impossible _MSC_VER check

Summary:
It is immediately preceded by this check:
  #if _MSC_VER < 1900
  #error "MSVC versions prior to Visual Studio 2015 are not supported"
  #endif

Reviewers: EricWF

Subscribers: christof, cfe-commits

Differential Revision: https://reviews.llvm.org/D45829

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@330360 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed