menuselect: Add DragonFly BSD.

In DragonFly BSD, added libraries from ports are placed into /usr/local.
Therefore, this directory must be added for the preprocessor, compiler, and
linker.

Beside that, the script ./configure was updated:
* OSARCH list was outdated and not used, removed.
* AC_CANONICAL_BUILD was not used.
* _REENTRANT, this feature test macro is obsolete.

ASTERISK-27820

Change-Id: I186d88d99cfa4de6569888e12ac97bd2f441c422