ninja windows: Support x64 configuration platform

pylib/gyp/generator/ninja.py

Index: pylib/gyp/generator/ninja.py
===================================================================
--- pylib/gyp/generator/ninja.py	(revision 1533)
+++ pylib/gyp/generator/ninja.py	(working copy)
@@ -378,8 +378,8 @@
     if self.flavor == 'win':
       self.msvs_settings = gyp.msvs_emulation.MsvsSettings(spec,
                                                            generator_flags)
-      target_platform = self.msvs_settings.GetTargetPlatform(config_name)
-      self.ninja.variable('arch', self.win_env[target_platform])
+      arch = self.msvs_settings.GetArch(config_name)
+      self.ninja.variable('arch', self.win_env[arch])
 
     # Compute predepends for all rules.
     # actions_depends is the dependencies this target depends on before running
@@ -798,7 +798,7 @@
       elif ext == 's' and self.flavor != 'win':  # Doesn't generate .o.d files.
         command = 'cc_s'
       elif (self.flavor == 'win' and ext == 'asm' and
-            self.msvs_settings.GetTargetPlatform(config_name) == 'Win32'):
+            self.msvs_settings.GetArch(config_name) == 'x86'):
         # Asm files only get auto assembled for x86 (not x64).
         command = 'asm'
         # Add the _asm suffix as msvs is capable of handling .cc and