Add support for Visual Studio 2026

Author: bellenot

cmake/modules/RootCPack.cmake

@@ -81,6 +81,8 @@ if(MSVC)
     math(EXPR VS_VERSION "${VC_MAJOR} - 3")
   elseif(MSVC_VERSION LESS 1950)
     math(EXPR VS_VERSION "${VC_MAJOR} - 2")
+  elseif(MSVC_VERSION LESS 1960)
+    math(EXPR VS_VERSION "${VC_MAJOR} - 1")
   else()
     message(FATAL_ERROR "MSVC_VERSION ${MSVC_VERSION} not implemented")
   endif()

interpreter/cling/lib/Utils/PlatformWin.cpp

@@ -386,6 +386,8 @@ static int GetVisualStudioVersionCompiledWith() {
   return 16;
 #elif (_MSC_VER < 1950)
   return 17;
+#elif (_MSC_VER < 1960)
+  return 18;
 #else
   #error "Unsupported/Untested _MSC_VER"
   // As of now this is what is should be...have fun!