cmGeneratorTarget: detect colliding target directories

Some projects might get unlucky and have targets which collide in the
sha3-512 hash (truncated to 4) in a directory which also collides in the
same way (easily done by sharing it). Note such problems as potentially
colliding and offer potential remedies.

Also add a test which generates the error.

Closes: #27465

Source/cmTarget.cxx

@@ -609,6 +609,7 @@ public:
   bool BuildInterfaceIncludesAppended;
   bool PerConfig;
   bool IsSymbolic;
+  bool IsForTryCompile{ false };
   cmTarget::Visibility TargetVisibility;
   std::set<BT<std::pair<std::string, bool>>> Utilities;
   std::set<std::string> CodegenDependencies;
@@ -2906,6 +2907,16 @@ bool cmTarget::CanCompileSources() const
   return false;
 }
 
+void cmTarget::SetIsForTryCompile()
+{
+  this->impl->IsForTryCompile = true;
+}
+
+bool cmTarget::IsForTryCompile() const
+{
+  return this->impl->IsForTryCompile;
+}
+
 char const* cmTarget::GetSuffixVariableInternal(
   cmStateEnums::ArtifactType artifact) const
 {