Set ZERO_AR_DATE=1 when running libtool.

pylib/gyp/mac_tool.py

Index: pylib/gyp/mac_tool.py
===================================================================
--- pylib/gyp/mac_tool.py	(revision 2014)
+++ pylib/gyp/mac_tool.py	(working copy)
@@ -223,11 +223,29 @@
         r'^.*libtool: warning for library: ' +
         r'.* the table of contents is empty ' +
         r'\(no object file members in the library define global symbols\)$')
-    libtoolout = subprocess.Popen(cmd_list, stderr=subprocess.PIPE)
+    env = os.environ.copy()
+    # Ref:
+    # http://www.opensource.apple.com/source/cctools/cctools-809/misc/libtool.c
+    # The problem with this flag is that it resets the file mtime on the file to
+    # epoch=0, e.g. 1970-1-1 or 1969-12-31 depending on daylight saving.

[M-A Ruel, 2014/12/11 00:41:35]

actually, s/daylight saving/timezone/

[Sébastien Marchand, 2014/12/11 18:37:45]

Done.

+    #
+    # We disable this for iOS as this cause a rebuild of all the library files.
+    is_ios_target = 'IPHONEOS_DEPLOYMENT_TARGET' in os.environ
+    if not is_ios_target:
+      env['ZERO_AR_DATE'] = '1'
+    libtoolout = subprocess.Popen(cmd_list, stderr=subprocess.PIPE, env=env)
     _, err = libtoolout.communicate()
     for line in err.splitlines():
       if not libtool_re.match(line) and not libtool_re5.match(line):
         print >>sys.stderr, line
+    # Unconditionally touch any file .a file on the command line if present if
+    # succeeded. A bit hacky.
+    if not is_ios_target and not libtoolout.returncode:
+      archives = [
+        cmd for cmd in cmd_list if cmd.endswith('.a') and os.path.isfile(cmd)
+      ]
+      if len(archives) == 1:
+        os.utime(archives[0], None)
     return libtoolout.returncode
 
   def ExecPackageFramework(self, framework, version):