after much struggle i have found the required package missing is ‘openssl-devel’. for asterisk 15 it wasnt required. but for asterisk 16 it is.
i didnt want to install all the different packages installed in the contrib/install_prereq. here is a minimal required prereq if anybody needs it -----
yum -y install epel-release kernel-devel make gcc gcc-c++ pkgconfig
#the default internal database is sqlite3
yum -y install sqlite-devel
;Asterisk requires libjansson >= 2.11 and no system copy was found.
;yum -y install jansson-devel
#to support --with-pjproject-bundled in asterisk we need additionally
yum -y install wget bzip2 patch libuuid-devel python-devel
#for default menuselect
yum -y install ncurses-devel libxml2-devel
#for odbc connection
yum -y install unixODBC-devel libtool-ltdl-devel
#for odbc postgresql
yum -y install postgresql-odbc
#utilities. note postgresql is for the client it is not the server.
yum -y install vim unzip sendmail postgresql-devel
#for ./configure ‘libedit-devel’
yum -y install libedit-devel
#shows an error in configure?
yum -y install file
#without it, chan_pjsip fails to load because of undefined symbol ast_sip_cli_traverse_objects
yum -y install openssl-devel