FreeTDM: Use ftdm_unused_arg() to silence -Wunused-argument warnings

Signed-off-by: Stefan Knoblich <stkn@openisdn.net>
FreeTDM: Silence -Wtautological-compare warnings emitted by clang

Fixes "warning: comparison of unsigned expression >= 0 is always true".

Signed-off-by: Stefan Knoblich <stkn@openisdn.net>
FreeTDM: Fix implicit conversion between enumeration types error

Full clang error message:

  error: implicit conversion from enumeration type 'ftdm_bool_t' to
  different enumeration type 'ftdm_status_t' [-Werror,-Wconversion]

Signed-off-by: Stefan Knoblich <stkn@openisdn.net>
FreeTDM: Move external ftmod_* library dependencies to _LIBADD

Making the build -Wl,--as-needed safe.
Tested on Centos 5.x + Gentoo.

Signed-off-by: Stefan Knoblich <stkn@openisdn.net>
FreeTDM: Make libpri pri_version() check -Wunused-but-set-variable safe

Signed-off-by: Stefan Knoblich <stkn@openisdn.net>
FreeTDM: ftmod_misdn uses clock_gettime() which is in librt, add a check

Fixes -Wl,-z,now / -Wl,-z,defs errors about undefined symbols.

Signed-off-by: Stefan Knoblich <stkn@openisdn.net>
FS-5403 --resolve