[build] Fix empty action inputs for xcode-ninja builds

src/v8.gyp

 # Copyright 2012 the V8 project authors. All rights reserved.
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 #       notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 #       copyright notice, this list of conditions and the following
 #       disclaimer in the documentation and/or other materials provided
@@ skipping 174 matching lines @@
         '<(SHARED_INTERMEDIATE_DIR)/experimental-libraries.cc',
         '<(SHARED_INTERMEDIATE_DIR)/extras-libraries.cc',
         '<(SHARED_INTERMEDIATE_DIR)/experimental-extras-libraries.cc',
         '<(INTERMEDIATE_DIR)/snapshot.cc',
       ],
       'actions': [
         {
           'action_name': 'run_mksnapshot',
           'inputs': [
             '<(mksnapshot_exec)',
-            '<(embed_script)',
-            '<(warmup_script)',
+          ],
+          'conditions': [
+            ['embed_script!=""', {
+              'inputs': [
+                '<(embed_script)',
+              ],
+            }],
+            ['warmup_script!=""', {
+              'inputs': [
+                '<(warmup_script)',
+              ],
+            }],
           ],
           'outputs': [
             '<(INTERMEDIATE_DIR)/snapshot.cc',
           ],
           'variables': {
             'mksnapshot_flags': [],
             'conditions': [
               ['v8_random_seed!=0', {
                 'mksnapshot_flags': ['--random-seed', '<(v8_random_seed)'],
               }],
@@ skipping 85 matching lines @@
           ],
           'sources': [
             'snapshot/natives-external.cc',
             'snapshot/snapshot-external.cc',
           ],
           'actions': [
             {
               'action_name': 'run_mksnapshot (external)',
               'inputs': [
                 '<(mksnapshot_exec)',
-                '<(embed_script)',
-                '<(warmup_script)',
               ],
               'variables': {
                 'mksnapshot_flags': [],
                 'conditions': [
                   ['v8_random_seed!=0', {
                     'mksnapshot_flags': ['--random-seed', '<(v8_random_seed)'],
                   }],
                   ['v8_vector_stores!=0', {
                     'mksnapshot_flags': ['--vector-stores'],
                   }],
                 ],
               },
               'conditions': [
+                ['embed_script!=""', {
+                  'inputs': [
+                    '<(embed_script)',
+                  ],
+                }],
+                ['warmup_script!=""', {
+                  'inputs': [
+                    '<(warmup_script)',
+                  ],
+                }],
                 ['want_separate_host_toolset==1', {
                   'target_conditions': [
                     ['_toolset=="host"', {
                       'outputs': [
                         '<(PRODUCT_DIR)/snapshot_blob_host.bin',
                       ],
                       'action': [
                         '<(mksnapshot_exec)',
                         '<@(mksnapshot_flags)',
                         '--startup_blob', '<(PRODUCT_DIR)/snapshot_blob_host.bin',
@@ skipping 1887 matching lines @@
         }],
         ['want_separate_host_toolset==1', {
           'toolsets': ['host'],
         }, {
           'toolsets': ['target'],
         }],
       ],
     },
   ],
 }