[build] Fix race in v8gen

tools/dev/v8gen.py

Index: tools/dev/v8gen.py
diff --git a/tools/dev/v8gen.py b/tools/dev/v8gen.py
index 69db399d191319575bcd3fe1866d8e29fd5e0a0b..f0fb74b7094608373c94beb88b0f48f0c9d5c995 100755
--- a/tools/dev/v8gen.py
+++ b/tools/dev/v8gen.py
@@ -265,6 +265,13 @@ class GenerateGnArgs(object):
       f.write('\n# Additional %s args:\n' % type)
       f.write(more_gn_args)
       f.write('\n')
+
+    # Artificially increment modification time as our modifications happen too
+    # fast. This makes sure that gn is properly rebuilding the ninja files.
+    mtime = os.path.getmtime(gn_args_path) + 1

[Michael Achenbach, 2016/09/22 09:08:28]

Really needs + 1, smaller increments don't trigger a rebuild. We also need to
open the file once more. Adding this logic to the open block above, doesn't lead
to the desired result either.

+    with open(gn_args_path, 'aw'):
+      os.utime(gn_args_path, (mtime, mtime))
+
     return True
 
   def main(self):