-fms-extensions: Bump the default _MSC_VER from 1700 to 1800, aka VS2013

VS 2013 is the minimum supported version, so it's reasonable for Clang
to simulate this by default. This also simplifies the clang-cl
self-host, since we have the 18.00 version check.

llvm-svn: 230243
diff --git a/clang/lib/Driver/Tools.cpp b/clang/lib/Driver/Tools.cpp
index 28279bb..c047375 100644
--- a/clang/lib/Driver/Tools.cpp
+++ b/clang/lib/Driver/Tools.cpp
@@ -4095,7 +4095,7 @@
       Ver = getMSCompatibilityVersion(MSCVersion->getValue());
 
     if (Ver.empty())
-      CmdArgs.push_back("-fms-compatibility-version=17.00");
+      CmdArgs.push_back("-fms-compatibility-version=18.00");
     else
       CmdArgs.push_back(Args.MakeArgString("-fms-compatibility-version=" + Ver));
   }