update gyp files to build on iOS

Note that there's a hack in SkImageDecoder_CG.cpp --
the necessary defines are included directly. This
is temporary until I can figure out how to include
them properly.
Review URL: https://codereview.appspot.com/6523044

git-svn-id: http://skia.googlecode.com/svn/trunk@5586 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gyp/xml.gyp b/gyp/xml.gyp
index 6650a5c..b7878e2 100644
--- a/gyp/xml.gyp
+++ b/gyp/xml.gyp
@@ -30,7 +30,7 @@
           '../src/xml/SkXMLPullParser.cpp', #if 0 around class decl in header
       ],
       'conditions': [
-        [ 'skia_os in ["win", "mac", "linux", "freebsd", "openbsd", "solaris", "android"]', {
+        [ 'skia_os in ["win", "mac", "linux", "freebsd", "openbsd", "solaris", "android", "ios"]', {
           'sources!': [
             # no jsapi.h by default on system
             '../include/xml/SkJS.h',