Add missing mac dependency on SystemConfiguration.framework

On MacOS, the policy::GetMachineName function in cloud_policy_util.cc
calls SCDynamicStoreCopyComputerName, and hence needs to link with
SystemConfiguration.framework. Add to the corresponding build target,
to not rely on unrelated build targets to import this framework.

Intended to enable reland of webrtc cl
https://webrtc-review.googlesource.com/c/src/+/148531,
which drops this library dependency from the rtc_base target.

Bug: webrtc:10857
Change-Id: Ifb1861348f1ecc480fb0f456f76597434900c9c1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1762071
Commit-Queue: Niels Möller <nisse@chromium.org>
Reviewed-by: Lutz Justen <ljusten@chromium.org>
Reviewed-by: Owen Min <zmin@chromium.org>
Auto-Submit: Niels Möller <nisse@chromium.org>
Cr-Commit-Position: refs/heads/master@{#688996}

components/policy/core/common/BUILD.gn

@@ -241,7 +241,10 @@ jumbo_source_set("internal") {
     ]
   }
   if (is_mac) {
-    libs = [ "CoreFoundation.framework" ]
+    libs = [
+      "CoreFoundation.framework",
+      "SystemConfiguration.framework",
+    ]
   }
   if (is_ios || is_mac) {
     sources += [