Both build options for symbol export can be specified

Bug: None
Change-Id: I26c421811952ded7382b48cbe970b97f4ed4d9e7
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/234640
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#35176}
diff --git a/AUTHORS b/AUTHORS
index 4ab41e0..cac58ca 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -102,6 +102,7 @@
 Stefan Gula <steweg@gmail.com>
 Stephan Hartmann <stha09@googlemail.com>
 Steve Reid <sreid@sea-to-sky.net>
+Takaaki Suzuki <takaakisuzuki.14@gmail.com>
 Tarun Chawla <trnkumarchawla@gmail.com>
 Todd Wong <todd.wong.ndq@gmail.com>
 Tomas Popela <tomas.popela@gmail.com>
diff --git a/BUILD.gn b/BUILD.gn
index 1a90c4b..6e7cd5d 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -119,10 +119,10 @@
   ldflags = []
 
   if (rtc_enable_symbol_export || is_component_build) {
-    defines = [ "WEBRTC_ENABLE_SYMBOL_EXPORT" ]
+    defines += [ "WEBRTC_ENABLE_SYMBOL_EXPORT" ]
   }
   if (rtc_enable_objc_symbol_export) {
-    defines = [ "WEBRTC_ENABLE_OBJC_SYMBOL_EXPORT" ]
+    defines += [ "WEBRTC_ENABLE_OBJC_SYMBOL_EXPORT" ]
   }
 
   if (build_with_mozilla) {