Can't compile nginx with SSL support, OpenSSL not found
Most likely you're missing the libssl-dev package.
But why not save yourself all the trouble and just use a PPA for nginx?
I used the following to get openssl for nginx:
https://ethitter.com/2016/06/nginx-openssl-1-0-2-http-2-alpn/
All other attempts either did not work, or were to clunky.
Hope this helps another...