Promote SQLite3 as a privatelib as it will also be used by mandoc

While here ensure sqlite3 is using pread(2) and enable the suppot for FTS4


git-svn-id: svn+ssh://svn.freebsd.org/base/head@274885 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
Forgot to update libmandoc


git-svn-id: svn+ssh://svn.freebsd.org/base/head@274886 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f