Fix -Wunreachable-code on Linux.

Starting from [1] the toolchain has started to enforce
-Wunreachable-code on Linux, this CL fixes the issues that are preventing
the Chromium roll into WebRTC.

Error example at [2].

[1] - https://chromium-review.googlesource.com/c/chromium/src/+/2093537
[2] - https://ci.chromium.org/p/webrtc/builders/try/linux_rel/34282?

Bug: webrtc:11448
Change-Id: I96e8901ae80c44d69143ed8d972e250b6b926a7d
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/171500
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#30858}

modules/audio_processing/BUILD.gn

@@ -540,6 +540,7 @@ if (rtc_include_tests) {
         "../../rtc_base:rtc_base_approved",
         "../../rtc_base:rtc_json",
         "../../rtc_base:task_queue_for_test",
+        "../../rtc_base/system:file_wrapper",
         "../../system_wrappers",
         "../../test:test_support",
         "aec_dump",