Extract functionality of test_main into separate library.

Extract functionality of test_main into separate library to be able to
reuse it if another main will be required.

Bug: webrtc:5996
Change-Id: I2925b4240bd0e4fb884b43bb16667ca2d6216bbd
Reviewed-on: https://webrtc-review.googlesource.com/c/105921
Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Artem Titov <titovartem@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25172}
diff --git a/modules/BUILD.gn b/modules/BUILD.gn
index 8127244..1df9865 100644
--- a/modules/BUILD.gn
+++ b/modules/BUILD.gn
@@ -236,6 +236,7 @@
     deps = [
       ":module_api",
       "../test:test_main",
+      "../test:test_support",
       "audio_coding:audio_coding_unittests",
       "audio_device:audio_device_unittests",
       "audio_mixer:audio_mixer_unittests",