build: move libcc patches to electron repo (#14104)

In the GN build, libchromiumcontent is no longer a distinct library, but
merely a container for a set of scripts and patches. Maintaining those
patches in a separate repository is tedious and error-prone, so merge
them into the main repo.

Once this is merged and GN is the default way to build Electron, the
libchromiumcontent repository can be archived.

patches/common/ffmpeg/.patches.yaml

@@ -0,0 +1,15 @@
+repo: src/third_party/ffmpeg
+patches:
+-
+  author: Ales Pergl <alpergl@microsoft.com>
+  file: build_gn.patch
+  description: |
+    Chromium's Mac toolchain sets the "install_name" linker parameter only
+    when "is_component_build" is true, but we want to set even if it's false,
+    because we are making a dylib which will be distributed inside a bundle.
+-
+  author: Aleksei Kuzmin <alkuzmin@microsoft.com>
+  file: fix_build_on_linux_x86.patch
+  description: |
+    Builds on Linux x86 fail with a clang error. See https://crbug.com/796379.
+    Once it's fixed the patch can be removed.

patches/common/ffmpeg/build_gn.patch

@@ -0,0 +1,15 @@
+diff --git a/BUILD.gn b/BUILD.gn
+index 5439b39693..6783292c3b 100755
+--- a/BUILD.gn
++++ b/BUILD.gn
+@@ -393,6 +393,10 @@ if (is_component_ffmpeg) {
+     # So we can append below and assume they're defined.
+     ldflags = []
+ 
++    if (!is_component_build && is_mac) {
++      ldflags += [ "-Wl,-install_name,@rpath/libffmpeg.dylib" ]
++    }
++
+     if (is_fuchsia || (is_posix && !is_mac)) {
+       # Fixes warnings PIC relocation when building as component.
+       ldflags += [

patches/common/ffmpeg/fix_build_on_linux_x86.patch

@@ -0,0 +1,13 @@
+diff --git a/BUILD.gn b/BUILD.gn
+index ff09111634..fa7712a3a3 100755
+--- a/BUILD.gn
++++ b/BUILD.gn
+@@ -247,7 +247,7 @@ target(link_target_type, "ffmpeg_internal") {
+     # On POSIX x86, sanitizers will fail to compiler the H264 CABAC code due to
+     # insufficient registers unless we disable EBP usage. crbug.com/786760
+     if (target_cpu == "x86") {
+-      if (using_sanitizer) {
++      if (using_sanitizer || is_electron_build) {
+         defines += [ "HAVE_EBP_AVAILABLE=0" ]
+       } else {
+         defines += [ "HAVE_EBP_AVAILABLE=1" ]