VS: Do not fail on Windows 10 with VS 2015 if no SDK is available (#15929)

Since commit v3.4.0-rc1~5^2~1 (VS: Add support for selecting the Windows
10 SDK, 2015-09-30) the VS 2015 generator requires a Windows 10 SDK to
be available when CMAKE_SYSTEM_VERSION specifies Windows 10 (e.g.  when
building on a Windows 10 host).  Howewver, it is possible to install VS
2015 without any Windows 10 SDK.  Instead of failing with an error
message about the lack of a Windows 10 SDK, simply tolerate this case
and use the default Windows 8.1 SDK.  Since building for Windows Store
still requires the SDK, retain the diagnostic in that case.

1 files changed, 5 insertions, 4 deletions

diff --git a/Source/cmGlobalVisualStudio14Generator.cxx b/Source/cmGlobalVisualStudio14Generator.cxx
index 83499f1..2f266cd 100644
--- a/Source/cmGlobalVisualStudio14Generator.cxx
+++ b/Source/cmGlobalVisualStudio14Generator.cxx
@@ -115,7 +115,7 @@ bool cmGlobalVisualStudio14Generator::InitializeWindows(cmMakefile* mf)
 {
   if (cmHasLiteralPrefix(this->SystemVersion, "10.0"))
     {
-    return this->SelectWindows10SDK(mf);
+    return this->SelectWindows10SDK(mf, false);
     }
   return true;
 }
@@ -143,17 +143,18 @@ bool cmGlobalVisualStudio14Generator::InitializeWindowsStore(cmMakefile* mf)
     }
   if (cmHasLiteralPrefix(this->SystemVersion, "10.0"))
     {
-    return this->SelectWindows10SDK(mf);
+    return this->SelectWindows10SDK(mf, true);
     }
   return true;
 }
 
 //----------------------------------------------------------------------------
-bool cmGlobalVisualStudio14Generator::SelectWindows10SDK(cmMakefile* mf)
+bool cmGlobalVisualStudio14Generator::SelectWindows10SDK(cmMakefile* mf,
+                                                         bool required)
 {
   // Find the default version of the Windows 10 SDK.
   this->WindowsTargetPlatformVersion = this->GetWindows10SDKVersion();
-  if (this->WindowsTargetPlatformVersion.empty())
+  if (required && this->WindowsTargetPlatformVersion.empty())
     {
     std::ostringstream  e;
     e << "Could not find an appropriate version of the Windows 10 SDK"