build: non-recursive ldpd

build: non-recursive ldpd

This also fixes a build problem where using #include
"ldpd/ldp_vty_cmds_clippy.c" results in the Makefile dependency tracking
having both

ldp_vty_cmds.c: ldp_vty_cmds_clippy.c
ldp_vty_cmds.c: ../ldpd/ldp_vty_cmds_clippy.c

(because, if it's included as "ldpd/..", it uses the "-I.." include path
in gcc, so the gcc -MD dependency output is "../ldpd/...")

... all of which causes the build to try to build it twice (at the same
time) and fail rather stupidly.

With a non-recursive build, the two paths are identical and everything
just works.

Signed-off-by: David Lamparter <equinox@opensourcerouting.org>