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/chromium/allow_new_privs.patch

@@ -0,0 +1,13 @@
+diff --git a/base/process/launch.h b/base/process/launch.h
+index 20b76fc..9db73bf 100644
+--- a/base/process/launch.h
++++ b/base/process/launch.h
+@@ -147,7 +147,7 @@ struct BASE_EXPORT LaunchOptions {
+ 
+   // By default, child processes will have the PR_SET_NO_NEW_PRIVS bit set. If
+   // true, then this bit will not be set in the new child process.
+-  bool allow_new_privs = false;
++  bool allow_new_privs = true;
+ 
+   // Sets parent process death signal to SIGKILL.
+   bool kill_on_parent_death = false;