Decoupling rtc_base from apple specific code [with cyclic deps]

webrtc/rtc_base/BUILD.gn

Index: webrtc/rtc_base/BUILD.gn
diff --git a/webrtc/rtc_base/BUILD.gn b/webrtc/rtc_base/BUILD.gn
index 925f915aca4efd600f1d7adca70b55e8ca99a08c..68299c343e6833de106dd7603bca8afcf8638482 100644
--- a/webrtc/rtc_base/BUILD.gn
+++ b/webrtc/rtc_base/BUILD.gn
@@ -398,6 +398,21 @@ rtc_source_set("rtc_json") {
   }
 }
 
+if (is_ios || is_mac) {
+  rtc_static_library("objc_rtc_base") {
+    check_includes = false
+    sources = [
+      "applefilesystem.mm",
+      "thread_darwin.mm",
+    ]
+
+    # We are explicitly disabling the check because we prefer to have a
+    # cyclic dependency instead of having to add an explicit dependency
+    # only for mac or ios on a lot of targets.
+    # deps = [ ":rtc_base" ]
+  }
+}
+
 rtc_static_library("rtc_base") {
   cflags = []
   cflags_cc = []
@@ -414,7 +429,6 @@ rtc_static_library("rtc_base") {
   all_dependent_configs = [ ":rtc_base_all_dependent_config" ]
 
   sources = [
-    "applefilesystem.mm",
     "asyncinvoker-inl.h",
     "asyncinvoker.cc",
     "asyncinvoker.h",
@@ -567,10 +581,8 @@ rtc_static_library("rtc_base") {
   }
 
   if (is_ios || is_mac) {
-    sources += [
-      "macifaddrs_converter.cc",
-      "thread_darwin.mm",
-    ]
+    sources += [ "macifaddrs_converter.cc" ]
+    deps += [ ":objc_rtc_base" ]
   }
 
   if (use_x11) {