Fix subscripting support.

Subscripting needs libarc_lite to works. To force compilation with this
library, the linker must have the -f-obj-arc parameter.

R=stuartmorgan@chromium.org

Review URL: https://chromiumcodereview.appspot.com/14850014

git-svn-id: http://src.chromium.org/svn/trunk/src/build@198428 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

common.gypi

@@ -4033,6 +4033,13 @@
                 },
               },
             },
+            'xcode_settings': {
+              # It is necessary to link with the -fobjc-arc flag to use
+              # subscripting on iOS < 6.
+              'OTHER_LDFLAGS': [
+                '-fobjc-arc',
+              ],
+            },
             'conditions': [
               # TODO(justincohen): ninja builds don't support signing yet.
               ['"<(GENERATOR)"!="ninja"', {