Allow use of SKIA_OUT on Windows

gyp_skia

Index: gyp_skia
===================================================================
--- gyp_skia	(revision 9919)
+++ gyp_skia	(working copy)
@@ -62,12 +62,10 @@
   if not output_dir:
     return os.path.join(os.path.abspath(script_dir), 'out')
 
-  if (os.name != 'posix' or
-     (sys.platform.startswith('darwin') and 
+  if (sys.platform.startswith('darwin') and 
       (not os.getenv('GYP_GENERATORS') or 
-       'make' not in os.getenv('GYP_GENERATORS')))):
-    print 'ERROR: variable SKIA_OUT is not valid on Mac (using xcodebuild)' \
-          ' or Windows'
+       'make' not in os.getenv('GYP_GENERATORS'))):
+    print 'ERROR: variable SKIA_OUT is not valid on Mac (using xcodebuild)'
     sys.exit(-1);
 
   if os.path.isabs(output_dir):