Rework miral::launch_app_env() even more to avoid calling functions that are not async-signal-safe after fork() (#3594)

Author: Saviq

src/miral/launch_app.cpp

@@ -151,11 +151,11 @@ auto miral::launch_app_env(
 
     if (pid == 0)
     {
-        mir::log_debug("Restoring sigmask");
         sigset_t all_signals;
         sigfillset(&all_signals);
         pthread_sigmask(SIG_UNBLOCK, &all_signals, nullptr);
 
+        // execvpe() isn't listed as being async-signal-safe, but the implementation looks fine and rewriting seems unnecessary
         execvpe(exec_args[0], const_cast<char*const*>(exec_args.data()), const_cast<char*const*>(exec_env.data()));
 
         mir::log_warning("Failed to execute client (\"%s\") error: %s", exec_args[0], strerror(errno));