Fix `warning: unknown pragma ignored` for mingw target

[mstorsjo]

LGTM, I can commit it for you.

[mstorsjo]

Committed, but I forgot to mention your name in the commit message - I'm truly sorry about that.

llvm/trunk/lib/Support/Windows/WindowsSupport.h

if (getVer) {
                                   info.dwBuildNumber);
       }
     }
   }
 
   OSVERSIONINFOEX info;
   ZeroMemory(&info, sizeof(OSVERSIONINFOEX));
   info.dwOSVersionInfoSize = sizeof(OSVERSIONINFOEX);
+#if defined(_MSC_VER)
 #pragma warning(push)
 #pragma warning(disable : 4996)
+#endif // _MSC_VER
   // Starting with Microsoft SDK for Windows 8.1, this function is deprecated
   // in favor of the new Windows Version Helper APIs.  Since we don't specify a
   // minimum SDK version, it's easier to simply disable the warning rather than
   // try to support both APIs.
   if (GetVersionEx((LPOSVERSIONINFO)&info) == 0)
     return llvm::VersionTuple();
+#if defined(_MSC_VER)
 #pragma warning(pop)
+#endif // _MSC_VER
 
   return llvm::VersionTuple(info.dwMajorVersion, info.dwMinorVersion, 0,
                             info.dwBuildNumber);
 }
 
 inline bool MakeErrMsg(std::string *ErrMsg, const std::string &prefix) {
   if (!ErrMsg)
     return true;