GN: Add missing config //webrtc:common_objc for rtc_sdk_common_objc

webrtc/sdk/BUILD.gn

Index: webrtc/sdk/BUILD.gn
diff --git a/webrtc/sdk/BUILD.gn b/webrtc/sdk/BUILD.gn
index 4cceb8e1a6e9ee29c012c23aabcf71037afb69f0..f4402c8b452b3a90b516cf44c829a849589c7102 100644
--- a/webrtc/sdk/BUILD.gn
+++ b/webrtc/sdk/BUILD.gn
@@ -27,7 +27,10 @@ if (is_ios || (is_mac && mac_deployment_target == "10.7")) {
     deps = [
       "../base:rtc_base",
     ]
-    configs += [ "//build/config/compiler:enable_arc" ]
+    configs += [
+      "..:common_objc",
+      "//build/config/compiler:enable_arc",

[tkchin_webrtc, 2016/10/06 20:50:38]

enable_arc should be a common objc config I think. There shouldn't be instances
of non-arc code for targets that currently use common_objc that I know of.

[kjellander_webrtc, 2016/10/07 05:09:29]

If that was possible we certainly should do that. However configs cannot include
other configs in GN, so it's not possible. The workaround for that would be to
introduce our own template for this, but that would mean at least two templates
since both rtc_static_library and rtc_test targets use this. So I won't do it in
this CL at least.

+    ]
     public_configs = [ ":rtc_sdk_common_objc_config" ]
     sources = [
       "objc/Framework/Classes/NSString+StdString.h",