Bug 1875201 - Add method for conditionally including media/libvpx/libvpx - moz.build file updates. r=ng,webrtc-reviewers

This patch is the result of running:

> ./mach python python/mozbuild/mozbuild/gn_processor.py \
>  dom/media/webrtc/third_party_build/gn-configs/webrtc.json

Differential Revision: https://phabricator.services.mozilla.com/D200118

CLOBBER

@@ -22,4 +22,4 @@
 # changes to stick? As of bug 928195, this shouldn't be necessary! Please
 # don't change CLOBBER for WebIDL changes any more.
 
-Modified build files in third_party/libwebrtc - Bug 1871981 - Vendor libwebrtc from fd3b346e27
+Modified build files in third_party/libwebrtc - turn off our 'fake' vpx build that only pointed to media/libvpx/libvpx

third_party/libwebrtc/modules/video_coding/webrtc_libvpx_interface_gn/moz.build

@@ -5,6 +5,9 @@
 
   ### This moz.build was AUTOMATICALLY GENERATED from a GN config,  ###
   ### DO NOT edit it by hand.                                       ###
+if not CONFIG["MOZ_SYSTEM_LIBVPX"]:
+    LOCAL_INCLUDES += [ "/media/libvpx/libvpx/" ]
+    CXXFLAGS += CONFIG["MOZ_LIBVPX_CFLAGS"]
 
 COMPILE_FLAGS["OS_INCLUDES"] = []
 AllowCompilerWarnings()
@@ -25,7 +28,6 @@ LOCAL_INCLUDES += [
     "!/ipc/ipdl/_ipdlheaders",
     "!/third_party/libwebrtc/gen",
     "/ipc/chromium/src",
-    "/media/libvpx/libvpx/",
     "/third_party/libwebrtc/",
     "/third_party/libwebrtc/third_party/abseil-cpp/",
     "/tools/profiler/public"

third_party/libwebrtc/modules/video_coding/webrtc_vp8_gn/moz.build

@@ -5,6 +5,9 @@
 
   ### This moz.build was AUTOMATICALLY GENERATED from a GN config,  ###
   ### DO NOT edit it by hand.                                       ###
+if not CONFIG["MOZ_SYSTEM_LIBVPX"]:
+    LOCAL_INCLUDES += [ "/media/libvpx/libvpx/" ]
+    CXXFLAGS += CONFIG["MOZ_LIBVPX_CFLAGS"]
 
 COMPILE_FLAGS["OS_INCLUDES"] = []
 AllowCompilerWarnings()
@@ -25,7 +28,6 @@ LOCAL_INCLUDES += [
     "!/ipc/ipdl/_ipdlheaders",
     "!/third_party/libwebrtc/gen",
     "/ipc/chromium/src",
-    "/media/libvpx/libvpx/",
     "/media/libyuv/",
     "/media/libyuv/libyuv/include/",
     "/third_party/libwebrtc/",

third_party/libwebrtc/modules/video_coding/webrtc_vp9_gn/moz.build

@@ -5,6 +5,9 @@
 
   ### This moz.build was AUTOMATICALLY GENERATED from a GN config,  ###
   ### DO NOT edit it by hand.                                       ###
+if not CONFIG["MOZ_SYSTEM_LIBVPX"]:
+    LOCAL_INCLUDES += [ "/media/libvpx/libvpx/" ]
+    CXXFLAGS += CONFIG["MOZ_LIBVPX_CFLAGS"]
 
 COMPILE_FLAGS["OS_INCLUDES"] = []
 AllowCompilerWarnings()
@@ -25,7 +28,6 @@ LOCAL_INCLUDES += [
     "!/ipc/ipdl/_ipdlheaders",
     "!/third_party/libwebrtc/gen",
     "/ipc/chromium/src",
-    "/media/libvpx/libvpx/",
     "/media/libyuv/",
     "/media/libyuv/libyuv/include/",
     "/third_party/libwebrtc/",

third_party/libwebrtc/moz.build

@@ -439,7 +439,6 @@ DIRS += [
     "/third_party/libwebrtc/third_party/abseil-cpp/absl/types/span_gn",
     "/third_party/libwebrtc/third_party/abseil-cpp/absl/types/variant_gn",
     "/third_party/libwebrtc/third_party/abseil-cpp/absl/utility/utility_gn",
-    "/third_party/libwebrtc/third_party/libvpx/libvpx_gn",
     "/third_party/libwebrtc/third_party/libyuv/libyuv_gn",
     "/third_party/libwebrtc/third_party/pffft/pffft_gn",
     "/third_party/libwebrtc/third_party/rnnoise/rnn_vad_gn",