databases/mariadb55-server: Fix FreeBSD 8 and 9 (jemallac issue)

Bring in MariaDB 10's jemalloc logic to fix FreeBSD 8 and 9.
While here, convert to USES+= execinfo

PR:		195320
Reported by:	FreeBSD 9 users
Submitted by:	maintainer
Final fix by:	marino


git-svn-id: svn+ssh://svn.freebsd.org/ports/head@373396 35697150-7ecd-e111-bb59-0022644237b5