Add missing RTC_EXPORT for the component build.

Bug: webrtc:9419
Change-Id: I3225259fb4cc55e9820f590928795f4587f1e3cb
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/153884
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29479}
diff --git a/rtc_base/BUILD.gn b/rtc_base/BUILD.gn
index 17cf3f5..564989a 100644
--- a/rtc_base/BUILD.gn
+++ b/rtc_base/BUILD.gn
@@ -58,6 +58,7 @@
     "../api:array_view",
     "../api:scoped_refptr",
     "system:arch",
+    "system:rtc_export",
     "system:unused",
     "third_party/base64",
     "//third_party/abseil-cpp/absl/types:optional",
@@ -311,6 +312,7 @@
   deps = [
     ":safe_compare",
     "system:inline",
+    "system:rtc_export",
     "//third_party/abseil-cpp/absl/meta:type_traits",
     "//third_party/abseil-cpp/absl/strings",
   ]
@@ -390,6 +392,7 @@
     ":checks",
     ":safe_conversions",
     ":stringutils",
+    "system:rtc_export",
   ]
   libs = []
   if (is_win) {
@@ -762,6 +765,7 @@
     "../api:scoped_refptr",
     "network:sent_packet",
     "system:file_wrapper",
+    "system:rtc_export",
     "third_party/base64",
     "third_party/sigslot",
     "//third_party/abseil-cpp/absl/algorithm:container",