Move rtc_base/ignore_wundef.h to its own target.

Since rtc_base/ignore_wundef.h doesn't have any dependency, it is easy to
move it to its own target and allow its dependant to avoid to take a
dependency rtc_base:on rtc_base_approved.

Bug: webrtc:9419
Change-Id: I17f205b0cb2b21cad388b04e60082df9398dffdf
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/157428
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29548}
diff --git a/rtc_tools/BUILD.gn b/rtc_tools/BUILD.gn
index 3e73f3a..5a8ffc3 100644
--- a/rtc_tools/BUILD.gn
+++ b/rtc_tools/BUILD.gn
@@ -280,6 +280,7 @@
       deps = [
         ":chart_proto",
         "../api:function_view",
+        "../rtc_base:ignore_wundef",
 
         # TODO(kwiberg): Remove this dependency.
         "../api/audio_codecs:audio_codecs_api",
@@ -442,6 +443,7 @@
         "../modules/audio_processing:audioproc_debug_proto",
         "../modules/audio_processing:audioproc_protobuf_utils",
         "../modules/audio_processing:audioproc_test_utils",
+        "../rtc_base:ignore_wundef",
         "../rtc_base:protobuf_utils",
         "../rtc_base:rtc_base_approved",
         "//third_party/abseil-cpp/absl/flags:flag",