VS15: Add Visual Studio 15 generator

Call the generator "Visual Studio 15" without any year because the
preview version of VS 15 does not provide a year in the product name.

Copy cmGlobalVisualStudio14Generator to cmGlobalVisualStudio15Generator
and update version numbers accordingly.  Add the VS15 enumeration value.
Note that we do not need to add a MSVC15 variable or v150 toolset
because Visual Studio 15 comes with an updated version of the v140
toolset and remains ABI-compatible.

Teach tests VSExternalInclude, RunCMake.GeneratorPlatform, and
RunCMake.GeneratorToolset to treat VS 15 as they do VS 10-14.

Closes: #16143

1 files changed, 2 insertions, 1 deletions

diff --git a/Source/cmGlobalVisualStudioGenerator.h b/Source/cmGlobalVisualStudioGenerator.h
index 1d456ffb65..3312ed6555 100644
--- a/Source/cmGlobalVisualStudioGenerator.h
+++ b/Source/cmGlobalVisualStudioGenerator.h
@@ -34,7 +34,8 @@ public:
     VS11 = 110,
     VS12 = 120,
     /* VS13 = 130 was skipped */
-    VS14 = 140
+    VS14 = 140,
+    VS15 = 150
   };
 
   cmGlobalVisualStudioGenerator(cmake* cm);