Update _MSC_VER equality checks for msdiaNNN.dll

Use inequality instead of equality to defend against minor version
increases in _MSC_VER. An _MSC_VER value of 1901 should still use
msdia140.dll, as described in this blog post:
https://blogs.msdn.microsoft.com/vcblog/2016/10/05/visual-c-compiler-version/

llvm-svn: 284058