fix(main/lighttpd): link with libandroid-spawn

[robertkirkman]

Progress on #21130

Fixes this error during build:

ld.lld: error: undefined symbol: posix_spawn_file_actions_init
>>> referenced by fdevent.c:495 (../src/src/fdevent.c:495)
>>>               src/test_mod.p/fdevent.c.o:(fdevent_fork_execve)

I tested this by using the docker container to cross-compile this package, then copying the .deb file to my aarch64 Android 10 device. I was able to successfully test the resulting program as a functioning web server at runtime after installing the .deb file by typing these commands (note: identical commands are also required for testing the previous build of the lighttpd package from the time of NDK revision 26 that's currently in the repositories, so I believe that my update most likely has equivalent functionality without any regression):

mkdir -p $PREFIX/var/log/lighttpd
mkdir -p $PREFIX/var/www/htdocs
echo 'hello lighttpd' > $PREFIX/var/www/htdocs/index.html
lighttpd -f $PREFIX/etc/lighttpd/lighttpd.conf

My Android 10 device's WiFi LAN local IP address is 192.168.120.74, so then I used a separate computer's web browser to go to this address: http://192.168.120.74:8080/index.html, where I am able to see the text I wrote into the index.html file, "hello lighttpd"