Testing no /DUNICODE assumptions with Win more configs bots.

This CL will avoid regressions after the cleanup done in
https://webrtc-review.googlesource.com/c/src/+/128904.

Bug: None
Change-Id: Id01f554a6fb0972139e7810b7523c91321398c0f
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/130100
Reviewed-by: Oleh Prypin <oprypin@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27328}
diff --git a/webrtc.gni b/webrtc.gni
index 3a89a9a..6ba8d0a 100644
--- a/webrtc.gni
+++ b/webrtc.gni
@@ -187,6 +187,14 @@
   # (they will still be included in libjingle_peerconnection_so.so and
   # WebRTC.framework)
   rtc_include_builtin_video_codecs = true
+
+  # When set to true and in a standalone build, it will undefine UNICODE and
+  # _UNICODE (which are always defined globally by the Chromium Windows
+  # toolchain).
+  # This is only needed for testing purposes, WebRTC wants to be sure it
+  # doesn't assume /DUNICODE and /D_UNICODE but that it explicitly uses
+  # wide character functions.
+  rtc_win_undef_unicode = false
 }
 
 if (!build_with_mozilla) {