Mark EnableMedia with RTC_EXPORT

Bug: webrtc:15574
Change-Id: I324f9694bfe41fa9831a24eb4e3c4373b43a9cbb
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/325523
Auto-Submit: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#41055}
diff --git a/api/BUILD.gn b/api/BUILD.gn
index a3b32bc..692c4f4 100644
--- a/api/BUILD.gn
+++ b/api/BUILD.gn
@@ -46,6 +46,7 @@
     "../call",
     "../media:rtc_audio_video",
     "../pc:media_factory",
+    "../rtc_base/system:rtc_export",
   ]
 }