IDL build: factor out global objects action into a GYP template

Source/bindings/scripts/scripts.gypi

Index: Source/bindings/scripts/scripts.gypi
diff --git a/Source/bindings/scripts/scripts.gypi b/Source/bindings/scripts/scripts.gypi
index ab5445e15460096e06474809edd3ff6ba1bd22ba..9bf033d7eee635bc7f20f112a6acb4efc8e07108 100644
--- a/Source/bindings/scripts/scripts.gypi
+++ b/Source/bindings/scripts/scripts.gypi
@@ -41,5 +41,19 @@
       'v8_types.py',
       'v8_utilities.py',
     ],
+
+    'conditions': [
+        # These scripts can skip writing generated files if they are identical
+        # to the already existing files, which avoids further build steps, like
+        # recompilation. However, a dependency (earlier build step) having a
+        # newer timestamp than an output (later build step) confuses some build
+        # systems, so only use this on ninja, which explicitly supports this use
+        # case (gyp turns all actions into ninja restat rules).
+        ['"<(GENERATOR)"=="ninja"', {
+          'write_file_only_if_changed': '1',
+        }, {
+          'write_file_only_if_changed': '0',
+        }],
+    ],
   },
 }