GN: Fix Windows Clang errors

tools/gyp_flag_compare.py

Index: tools/gyp_flag_compare.py
diff --git a/tools/gyp_flag_compare.py b/tools/gyp_flag_compare.py
index 0c17b1a3356cc0298eb25353a76a3085c13875a0..b4432ba1254f3998319a23d35437b7508aec283d 100755
--- a/tools/gyp_flag_compare.py
+++ b/tools/gyp_flag_compare.py
@@ -113,7 +113,7 @@ def CountsByDirname(dict_of_list):
 class Comparison(object):
   """A comparison of the currently-configured build for a target."""
 
-  def __init__(self, gyp_target, gn_target=None, gyp_dir=_DEFAULT_GYP_DIR,
+  def __init__(self, gyp_target=None, gn_target=None, gyp_dir=_DEFAULT_GYP_DIR,
                gn_dir=_DEFAULT_GN_DIR):
     """Creates a comparison of a GN and GYP target. If the target names differ
     between the two build systems, then two names may be passed.
@@ -195,8 +195,13 @@ class Comparison(object):
       print >> sys.stderr, 'Building in %s...' % self._gyp_dir
       Run('ninja -C %s -d keeprsp %s' % (self._gyp_dir, self._gn_target))
 
-    gn = Run('ninja -C %s -t commands %s' % (self._gn_dir, self._gn_target))
-    gyp = Run('ninja -C %s -t commands %s' % (self._gyp_dir, self._gyp_target))
+    if self._gn_target is not None:
+      gn = Run('ninja -C %s -t commands %s' % (self._gn_dir, self._gn_target))
+      gyp = Run('ninja -C %s -t commands %s' % (self._gyp_dir,
+                                                self._gyp_target))
+    else:
+      gn = Run('ninja -C %s -t commands' % (self._gn_dir))
+      gyp = Run('ninja -C %s -t commands' % (self._gyp_dir))
 
     self._gn_flags = self._GetFlags(gn.splitlines(),
                                     os.path.join(os.getcwd(), self._gn_dir))
@@ -389,7 +394,7 @@ def Run(command_line):
 
 
 def main():
-  if len(sys.argv) < 4:
+  if len(sys.argv) < 3:
     print 'usage: %s gyp_dir gn_dir target' % __file__
     print '   or: %s gyp_dir gn_dir gyp_target gn_target' % __file__
     return 1
@@ -397,10 +402,13 @@ def main():
   gyp_dir = sys.argv[1]
   gn_dir = sys.argv[2]
 
-  gyp_target = sys.argv[3]
+  gyp_target = gn_target = None
+
   if len(sys.argv) == 4:
+    gyp_target = sys.argv[3]
     gn_target = gyp_target
-  else:
+  elif len(sys.argv) == 5:
+    gyp_target = sys.argv[3]
     gn_target = sys.argv[4]
 
   print 'GYP output directory is %s' % gyp_dir