Adds `read_first_line.cc` and `read_first_line.hh` to CMake.
Adds `read_first_line.cc` and `read_first_line.hh` to CMake.

Target `httpd` was failing when generating using CMake due to missing `util/read_first_line.cc/.hh`. This patch adds them in the CMake recipe.

Message-Id: <45f9c9c19398a398fe058109e1a5f428b4fa2e50@gmail.com>

syuu1228/seastar,avikivity/seastar,syuu1228/seastar,cloudius-systems/seastar,dreamsxin/seastar,scylladb/seastar,scylladb/seastar,dreamsxin/seastar,avikivity/seastar,avikivity/seastar,cloudius-systems/seastar,scylladb/seastar,syuu1228/seastar,cloudius-systems/seastar,dreamsxin/seastar