Core: fixed environment variables on exit. Similarly to 6822:c045b4926b2c, environment variables introduced with the "env" directive (and "NGINX_BPF_MAPS" added by QUIC) are now allocated via ngx_alloc(), and explicitly freed by a cleanup handler if no longer used. In collaboration with Sergey Kandaurov.

# Copyright (C) Igor Sysoev
# Copyright (C) Nginx, Inc.


cat << END >> $NGX_AUTO_CONFIG_H

#ifndef $have
#define $have  $value
#endif

END