[CallbackList] Support component build

Bug: webrtc:11943
Change-Id: I2abde42d65bc66f8e026fedfc2aa26bf86e1e46d
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/258600
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Tomas Gunnarsson <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#36516}
diff --git a/rtc_base/BUILD.gn b/rtc_base/BUILD.gn
index 2295b2d..5b3776a 100644
--- a/rtc_base/BUILD.gn
+++ b/rtc_base/BUILD.gn
@@ -71,6 +71,7 @@
     "../api:function_view",
     "system:assume",
     "system:inline",
+    "system:rtc_export",
   ]
 }