Fix the build of DIASession.cpp on Windows with VS 2017 + DIA SDK.

On VS 2017, _MSC_VER is > 1910, and so the build fails with the following
error:

    Unknown Visual Studio version

The fix is based on the sources of LLVM 5.0, where this has been fixed:

    https://github.com/llvm-mirror/llvm/blob/master/lib/DebugInfo/PDB/DIA/DIASession.cpp#L76

The reason we were unable to reproduce this build issue is that when you open
llvm/src/lib/DebugInfo/PDB/CMakeLists.txt, you can see that DIASession.cpp is
built only if you have Debug Interface Access SDK (DIA SDK) in your system.

For more information, see the following issues:
* https://github.com/avast-tl/fileformat/issues/4
* avast/retdec#61

Author: s3rvac

src/lib/DebugInfo/PDB/DIA/DIASession.cpp

@@ -58,9 +58,9 @@ Error LoadDIA(CComPtr<IDiaDataSource> &DiaDataSource) {
 #endif
 
   const wchar_t *msdia_dll = nullptr;
-#if _MSC_VER == 1900
+#if _MSC_VER >= 1900 && _MSC_VER < 2000
   msdia_dll = L"msdia140.dll"; // VS2015
-#elif _MSC_VER == 1800
+#elif _MSC_VER >= 1800
   msdia_dll = L"msdia120.dll"; // VS2013
 #else
 #error "Unknown Visual Studio version."