Extract fft4g into separate build target

common_audio/fft4g.c is third party codem that have to be moved into
third_party folder, so to be able to do it at first we have to extract
it into separate target. It is extracted with corresponding header file
and will be moved in futher CL.

Bug: webrtc:8366
Change-Id: I586ca94d4e9242c23163b987fa334dfa705020ed
Reviewed-on: https://webrtc-review.googlesource.com/85372
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Artem Titov <titovartem@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23742}

common_audio/BUILD.gn

@@ -61,6 +61,7 @@ rtc_static_library("common_audio") {
 
   deps = [
     ":common_audio_c",
+    ":fft4g",
     ":sinc_resampler",
     "..:webrtc_common",
     "../:typedefs",
@@ -130,8 +131,6 @@ rtc_source_set("common_audio_c_arm_asm") {
 rtc_source_set("common_audio_c") {
   visibility += webrtc_default_visibility
   sources = [
-    "fft4g.c",
-    "fft4g.h",
     "ring_buffer.c",
     "ring_buffer.h",
     "signal_processing/auto_corr_to_refl_coef.c",
@@ -216,6 +215,7 @@ rtc_source_set("common_audio_c") {
   deps = [
     ":common_audio_c_arm_asm",
     ":common_audio_cc",
+    ":fft4g",
     "..:webrtc_common",
     "../:typedefs",
     "../rtc_base:checks",
@@ -227,6 +227,14 @@ rtc_source_set("common_audio_c") {
   ]
 }
 
+rtc_source_set("fft4g") {
+  visibility += webrtc_default_visibility
+  sources = [
+    "fft4g.c",
+    "fft4g.h",
+  ]
+}
+
 rtc_source_set("common_audio_cc") {
   sources = [
     "signal_processing/dot_product_with_scale.cc",

modules/audio_processing/BUILD.gn

@@ -123,6 +123,7 @@ rtc_static_library("audio_processing") {
     "../../api/audio:echo_control",
     "../../audio/utility:audio_frame_operations",
     "../../common_audio:common_audio_c",
+    "../../common_audio:fft4g",
     "../../rtc_base:checks",
     "../../rtc_base:deprecation",
     "../../rtc_base:gtest_prod",
@@ -268,6 +269,7 @@ rtc_source_set("audio_processing_c") {
     "../..:webrtc_common",
     "../../common_audio",
     "../../common_audio:common_audio_c",
+    "../../common_audio:fft4g",
     "../../rtc_base:checks",
     "../../rtc_base:rtc_base_approved",
     "../../system_wrappers:cpu_features_api",

modules/audio_processing/vad/BUILD.gn

@@ -39,6 +39,7 @@ rtc_static_library("vad") {
     "../../../audio/utility:audio_frame_operations",
     "../../../common_audio",
     "../../../common_audio:common_audio_c",
+    "../../../common_audio:fft4g",
     "../../../rtc_base:checks",
     "../../audio_coding:isac_vad",
   ]