VS: Suppress MSBuild default flags not specified by project or user

`Microsoft.Cl.Common.props` adds some `cl` flags by default, but for
CMake they may not match what's produced by command-line generators.
If the `-Zc:wchar_t`, `-Zc:forScope`, and/or `-Zc:inline` flags are
not specified by the project or user, suppress them.

Fixes: #26964

Source/cmVisualStudio10TargetGenerator.cxx

@@ -3632,18 +3632,27 @@ bool cmVisualStudio10TargetGenerator::ComputeClOptions(
     if (!clOptions.HasFlag("BasicRuntimeChecks")) {
       clOptions.AddFlag("BasicRuntimeChecks", "Default");
     }
+    if (!clOptions.HasFlag("ForceConformanceInForLoopScope")) {
+      clOptions.AddFlag("ForceConformanceInForLoopScope", "");
+    }
     if (!clOptions.HasFlag("MinimalRebuild")) {
       clOptions.AddFlag("MinimalRebuild", "");
     }
     if (!clOptions.HasFlag("Optimization")) {
       clOptions.AddFlag("Optimization", "");
     }
+    if (!clOptions.HasFlag("RemoveUnreferencedCodeData")) {
+      clOptions.AddFlag("RemoveUnreferencedCodeData", "");
+    }
     if (!clOptions.HasFlag("RuntimeLibrary")) {
       clOptions.AddFlag("RuntimeLibrary", "");
     }
     if (!clOptions.HasFlag("SupportJustMyCode")) {
       clOptions.AddFlag("SupportJustMyCode", "");
     }
+    if (!clOptions.HasFlag("TreatWChar_tAsBuiltInType")) {
+      clOptions.AddFlag("TreatWChar_tAsBuiltInType", "");
+    }
   }
 
   this->ClOptions[configName] = std::move(pOptions);

Tests/RunCMake/VS10Project/RunCMakeTest.cmake

@@ -34,6 +34,7 @@ run_cmake(VsCSharpReferenceProps)
 run_cmake(VsCSharpWithoutSources)
 run_cmake(VsCSharpDeployFiles)
 run_cmake(VSCSharpDefines)
+run_cmake(VsDefaultFlags)
 run_cmake(VsSdkDirectories)
 run_cmake(VsGlobals)
 run_cmake(VsProjectImport)

Tests/RunCMake/VS10Project/VsDefaultFlags-check.cmake

@@ -0,0 +1,41 @@
+macro(VsDefaultFlags_check tgt)
+  set(vcProjectFile "${RunCMake_TEST_BINARY_DIR}/${tgt}.vcxproj")
+  if(NOT EXISTS "${vcProjectFile}")
+    set(RunCMake_TEST_FAILED "Project file ${tgt}.vcxproj does not exist.")
+    return()
+  endif()
+
+  set(HAVE_ForceConformanceInForLoopScope 0)
+  set(HAVE_RemoveUnreferencedCodeData 0)
+  set(HAVE_TreatWChar_tAsBuiltInType 0)
+
+  file(STRINGS "${vcProjectFile}" lines)
+  foreach(line IN LISTS lines)
+    if(line MATCHES "^ *<ForceConformanceInForLoopScope></ForceConformanceInForLoopScope>")
+      set(HAVE_ForceConformanceInForLoopScope 1)
+    endif()
+    if(line MATCHES "^ *<RemoveUnreferencedCodeData></RemoveUnreferencedCodeData>")
+      set(HAVE_RemoveUnreferencedCodeData 1)
+    endif()
+    if(line MATCHES "^ *<TreatWChar_tAsBuiltInType></TreatWChar_tAsBuiltInType>")
+      set(HAVE_TreatWChar_tAsBuiltInType 1)
+    endif()
+  endforeach()
+
+  if(NOT HAVE_ForceConformanceInForLoopScope)
+    set(RunCMake_TEST_FAILED "Project file ${tgt}.vcxproj does not have a <ForceConformanceInForLoopScope> property.")
+    return()
+  endif()
+
+  if(NOT HAVE_RemoveUnreferencedCodeData)
+    set(RunCMake_TEST_FAILED "Project file ${tgt}.vcxproj does not have a <RemoveUnreferencedCodeData> property.")
+    return()
+  endif()
+
+  if(NOT HAVE_TreatWChar_tAsBuiltInType)
+    set(RunCMake_TEST_FAILED "Project file ${tgt}.vcxproj does not have a <TreatWChar_tAsBuiltInType> property.")
+    return()
+  endif()
+endmacro()
+
+VsDefaultFlags_check(empty)

Tests/RunCMake/VS10Project/VsDefaultFlags.cmake

@@ -0,0 +1,2 @@
+enable_language(C)
+add_library(empty empty.c)