Ninja: Fix non-determinism in generated build statement order (#15968)

Generate custom command build statements in the order we encounter
source files specifying them.  Do not depend on pointer values of
internally allocated structures for ordering.

Source/cmLocalNinjaGenerator.cxx

@@ -454,13 +454,24 @@ cmLocalNinjaGenerator::WriteCustomCommandBuildStatement(
 void cmLocalNinjaGenerator::AddCustomCommandTarget(cmCustomCommand const* cc,
                                                    cmGeneratorTarget* target)
 {
-  this->CustomCommandTargets[cc].insert(target);
+  CustomCommandTargetMap::value_type v(cc, std::set<cmGeneratorTarget*>());
+  std::pair<CustomCommandTargetMap::iterator, bool>
+    ins = this->CustomCommandTargets.insert(v);
+  if (ins.second)
+    {
+    this->CustomCommands.push_back(cc);
+    }
+  ins.first->second.insert(target);
 }
 
 void cmLocalNinjaGenerator::WriteCustomCommandBuildStatements()
 {
-  for (CustomCommandTargetMap::iterator i = this->CustomCommandTargets.begin();
-       i != this->CustomCommandTargets.end(); ++i) {
+  for (std::vector<cmCustomCommand const*>::iterator vi =
+       this->CustomCommands.begin(); vi != this->CustomCommands.end(); ++vi)
+    {
+    CustomCommandTargetMap::iterator i = this->CustomCommandTargets.find(*vi);
+    assert(i != this->CustomCommandTargets.end());
+
     // A custom command may appear on multiple targets.  However, some build
     // systems exist where the target dependencies on some of the targets are
     // overspecified, leading to a dependency cycle.  If we assume all target

Source/cmLocalNinjaGenerator.h

@@ -106,6 +106,7 @@ private:
   typedef std::map<cmCustomCommand const*, std::set<cmGeneratorTarget*> >
     CustomCommandTargetMap;
   CustomCommandTargetMap CustomCommandTargets;
+  std::vector<cmCustomCommand const*> CustomCommands;
 };
 
 #endif // ! cmLocalNinjaGenerator_h