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/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" ]