flush runtime diagnostics promptly

src/linux_fastcgi.cpp

@@ -1467,6 +1467,10 @@ void init_base_process()
 
 int main(int argc, char** argv)
 {
+	// systemd connects stdout to a pipe, which otherwise block-buffers child
+	// diagnostics and assigns stale failures a misleading later journal time.
+	setvbuf(stdout, 0, _IOLBF, 0);
+	setvbuf(stderr, 0, _IONBF, 0);
 	// Warm up libgcc's backtrace state so the first in-handler backtrace()
 	// after a fault does not allocate.
 	backtrace(request_fault_frames, 4);