Ninja Multi-Config: Fix cross-config custom command dependency tracing

Process `CMAKE_CROSS_CONFIGS` and friends to properly configure the
generator for cross-config behavior before custom command dependency
tracing.

Source/cmGlobalGenerator.cxx

@@ -1402,6 +1402,9 @@ bool cmGlobalGenerator::Compute()
                                          this->SupportsDefaultConfigs())) {
     return false;
   }
+  if (!this->InspectConfigTypeVariables()) {
+    return false;
+  }
 
   // Some generators track files replaced during the Generate.
   // Start with an empty vector:

Source/cmGlobalGenerator.h

@@ -153,6 +153,8 @@ public:
    */
   virtual void Configure();
 
+  virtual bool InspectConfigTypeVariables() { return true; }
+
   bool Compute();
   virtual void AddExtraIDETargets() {}
 

Source/cmGlobalNinjaGenerator.cxx

@@ -568,9 +568,6 @@ void cmGlobalNinjaGenerator::Generate()
                                            msg.str());
     return;
   }
-  if (!this->InspectConfigTypeVariables()) {
-    return;
-  }
   if (!this->OpenBuildFileStreams()) {
     return;
   }

Source/cmGlobalNinjaGenerator.h

@@ -481,8 +481,6 @@ protected:
     const std::set<std::string>& all, const std::set<std::string>& defaults,
     const std::vector<std::string>& items);
 
-  virtual bool InspectConfigTypeVariables() { return true; }
-
   std::set<std::string> CrossConfigs;
   std::set<std::string> DefaultConfigs;
   std::string DefaultFileConfig;