VS: Change CMAKE_VS_WINRT_BY_DEFAULT to not implicitly enable WinRT

Original behaviour would unconditionally enable WinRT for all projects
so source file flag generation code can acknowledge WinRT being present
and disable it for C language source files.  An unintentional result of
that approach is that WinRT is enabled for ALL projects, including C++
projects/source files with no way to disable it

Instead use `CMAKE_VS_WINRT_BY_DEFAULT` as a hint that the platform is
WinRT-by-default and set global `CompileAsWinRT` flag to `false` unless
it was explicitly requested by either `WINRT_COMPONENT` option or `/ZW`
compilation option - similar to what Windows Phone/Windows Store
platform logic does

In case WinRT compilation is enabled for a project by either of
aforementioned methods, C language source file override logic will still
kick in and disable CompileAsWinRT for C source files

Fixes: #20063

1 files changed, 4 insertions, 5 deletions

diff --git a/Source/cmVisualStudio10TargetGenerator.cxx b/Source/cmVisualStudio10TargetGenerator.cxx
index 8fc40a79..5e005ea 100644
--- a/Source/cmVisualStudio10TargetGenerator.cxx
+++ b/Source/cmVisualStudio10TargetGenerator.cxx
@@ -2832,10 +2832,8 @@ bool cmVisualStudio10TargetGenerator::ComputeClOptions(
   }
 
   if (this->MSTools) {
-    // If we have the VS_WINRT_COMPONENT or CMAKE_VS_WINRT_BY_DEFAULT
-    // set then force Compile as WinRT.
-    if (this->GeneratorTarget->GetPropertyAsBool("VS_WINRT_COMPONENT") ||
-        this->Makefile->IsOn("CMAKE_VS_WINRT_BY_DEFAULT")) {
+    // If we have the VS_WINRT_COMPONENT set then force Compile as WinRT
+    if (this->GeneratorTarget->GetPropertyAsBool("VS_WINRT_COMPONENT")) {
       clOptions.AddFlag("CompileAsWinRT", "true");
       // For WinRT components, add the _WINRT_DLL define to produce a lib
       if (this->GeneratorTarget->GetType() == cmStateEnums::SHARED_LIBRARY ||
@@ -2843,7 +2841,8 @@ bool cmVisualStudio10TargetGenerator::ComputeClOptions(
         clOptions.AddDefine("_WINRT_DLL");
       }
     } else if (this->GlobalGenerator->TargetsWindowsStore() ||
-               this->GlobalGenerator->TargetsWindowsPhone()) {
+               this->GlobalGenerator->TargetsWindowsPhone() ||
+               this->Makefile->IsOn("CMAKE_VS_WINRT_BY_DEFAULT")) {
       if (!clOptions.IsWinRt()) {
         clOptions.AddFlag("CompileAsWinRT", "false");
       }