Change a return back to an _exit(1). It's not different functionally …

…but I decided it's more clear.

docs/signal-safe-tracing.md

@@ -165,7 +165,7 @@ void do_signal_safe_trace(cpptrace::frame_ptr* buffer, std::size_t count) {
         const char* exec_failure_message = "exec(signal_tracer) failed: Make sure the signal_tracer executable is in "
             "the current working directory and the binary's permissions are correct.\n";
         write(STDERR_FILENO, exec_failure_message, strlen(exec_failure_message));
-        return;
+        _exit(1);
     }
     // Resolve to safe_object_frames and write those to the pipe
     for(std::size_t i = 0; i < count; i++) {