Migrated RTPchange Gyp target to GN.

BUG=6162

Review-Url: https://codereview.webrtc.org/2194213002
Cr-Commit-Position: refs/heads/master@{#13601}
diff --git a/webrtc/modules/audio_coding/BUILD.gn b/webrtc/modules/audio_coding/BUILD.gn
index 98047fd..79381fc 100644
--- a/webrtc/modules/audio_coding/BUILD.gn
+++ b/webrtc/modules/audio_coding/BUILD.gn
@@ -1305,6 +1305,18 @@
     }
   }
 
+  executable("RTPchange") {
+    testonly = true
+
+    sources = [
+      "neteq/test/RTPchange.cc",
+    ]
+
+    deps = [
+      ":neteq_test_tools",
+    ]
+  }
+
   executable("rtp_analyze") {
     testonly = true