VS: Tell VS 16.4 not to verify CMake-provided custom command outputs

Extend the fix from commit 0578239d3a (VS: Tell VS 16.4 not to verify
SYMBOLIC custom command outputs, 2019-09-23, v3.15.4~2^2) to apply to
outputs in CMake-provided targets like `install`.  Simply mark these
outputs as `SYMBOLIC` too since they are not actually generated.

Fixes: #19737

Source/cmLocalVisualStudio7Generator.cxx

@@ -98,6 +98,10 @@ void cmLocalVisualStudio7Generator::FixGlobalTargets()
       std::string no_main_dependency;
       std::string force = cmStrCat(this->GetCurrentBinaryDirectory(),
                                    "/CMakeFiles/", l->GetName(), "_force");
+      if (cmSourceFile* sf =
+            this->Makefile->GetOrCreateGeneratedSource(force)) {
+        sf->SetProperty("SYMBOLIC", "1");
+      }
       if (cmSourceFile* file = this->Makefile->AddCustomCommandToOutput(
             force.c_str(), no_depends, no_main_dependency, force_commands, " ",
             0, true)) {