Perl: avoid returning 500 if header was already sent. Returning NGX_HTTP_INTERNAL_SERVER_ERROR if a perl code died after sending header will lead to a "header already sent" alert. To avoid it, we now check if header was already sent, and return NGX_ERROR instead if it was.

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


cat << END >> $NGX_AUTO_CONFIG_H

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

END