You could look at the configure.ac in ntp-dev (or any recent ntp-stable), say:
http://ntp.bkbits.net:8080/ntp-dev/configure.ac?REV=4b6a0c4clgted0re5ogPZQx0QgLLPw and find the hunk of code starting with: AC_MSG_CHECKING([for openssl include directory]) and decide for yourself if there is a better way to go... H
