[MS] Raise the default value of _MSC_VER to 1910, which is in VS 2017

[rnk]

Summary

This raises our default past 1900, which controls whether char16_t is a
builtin type or not.

Implements PR34243

[thakis]

Thanks!

Should probably get a release note too.

[rnk]

• go to 1911, 1910 was the preview
• add release notes

[STL_MSFT]

FYI: 1910 was the value for VS 2017 RTM. 1911 is the value for VS 2017 15.3, the first toolset update. 1912 will be the value for VS 2017 15.5, the second toolset update.

[rnk]

In D38646#892246, @STL_MSFT wrote:

FYI: 1910 was the value for VS 2017 RTM. 1911 is the value for VS 2017 15.3, the first toolset update. 1912 will be the value for VS 2017 15.5, the second toolset update.

Yep. The initial draft of this patch had the wrong commit message, but everything is fixed in the committed version.

I had 1910 installed on my machine locally, and spent this morning untangling that. Apparently now you have to install updates through the VS "Tools -> Extesions & Updates -> mumble" menu. Downloading and running the VS update 3 installer isn't enough.

cfe/trunk/docs/ReleaseNotes.rst

- ``-Wnull-pointer-arithmetic`` now warns about performing pointer arithmetic
   treated as a cast from integer to pointer (GNU extension).
 
 Non-comprehensive list of changes in this release
 -------------------------------------------------
 
 - Bitrig OS was merged back into OpenBSD, so Bitrig support has been
   removed from Clang/LLVM.
 
+- The default value of _MSC_VER was raised from 1800 to 1911, making it
+  compatible with the Visual Studio 2015 and 2017 C++ standard library headers.
+  Users should generally expect this to be regularly raised to match the most
+  recently released version of the Visual C++ compiler.
+
 New Compiler Flags
 ------------------
 
 - --autocomplete was implemented to obtain a list of flags and its arguments. This is used for shell autocompletion.
 
 Deprecated Compiler Flags
 -------------------------
 

cfe/trunk/lib/Driver/ToolChains/MSVC.cpp

VersionTuple MSVCToolChain::computeMSVCVersion(const Driver *D,
   VersionTuple MSVT = ToolChain::computeMSVCVersion(D, Args);
   if (MSVT.empty())
     MSVT = getMSVCVersionFromTriple(getTriple());
   if (MSVT.empty() && IsWindowsMSVC)
     MSVT = getMSVCVersionFromExe(getSubDirectoryPath(SubDirectoryType::Bin));
   if (MSVT.empty() &&
       Args.hasFlag(options::OPT_fms_extensions, options::OPT_fno_ms_extensions,
                    IsWindowsMSVC)) {
-    // -fms-compatibility-version=18.00 is default.
-    // FIXME: Consider bumping this to 19 (MSVC2015) soon.
-    MSVT = VersionTuple(18);
+    // -fms-compatibility-version=19.11 is default, aka 2017
+    MSVT = VersionTuple(19, 11);
   }
   return MSVT;
 }
 
 std::string
 MSVCToolChain::ComputeEffectiveClangTriple(const ArgList &Args,
                                            types::ID InputType) const {
   // The MSVC version doesn't care about the architecture, even though it